The Proceedings of the National Academy of Sciences USA (PNAS) publishes research reports, commentaries, perspectives, and colloquium papers. In accordance with the guiding principles established by George Ellery Hale in 1914, PNAS publishes brief first announcements of Academy members' and foreign associates' (hereafter referred to as members) more important contributions to research and of work that appears to a member to be of particular importance. PNAS is a general science journal with a broad scientific audience. All papers should be intelligible to this audience.

Research Reports describe the results of original research of exceptional importance.

Feature Articles are in-depth research reports with exceptional breadth. Features may be slightly longer than a regular research article to fully develop and present the findings.

Commentaries call attention to papers of particular note and are written at the invitation of the Editorial Board.

Perspectives present a viewpoint on an important area of research and are written only at the invitation of the Editorial Board. Perspectives focus on a specific field or subfield within a larger discipline and discuss current advances and future directions. Perspectives are of broad interest for nonspecialists and may add personal insight to a field.

Colloquium Papers are reports of scientific colloquia held under Academy auspices.

Letters are brief online-only comments that contribute to the discussion of a PNAS research article published within the last 3 months. Letters may not include requests to cite the letter writer's work, accusations of misconduct, or personal comments to an author. As of April 2009, letters are limited to 500 words and no more than 5 references.

The standard mode of transmitting manuscripts is for authors to submit them directly to PNAS. Authors must recommend 3 appropriate Editorial Board members, 3 NAS members who are expert in the paper's scientific area, and 5 qualified referees. The Board may choose someone who is or is not on that list or may reject the paper without further review. A directory of PNAS member editors and their research interests is available at http://nrc88.nas.edu/pnas_search. The editor may obtain reviews of the paper from at least 2 qualified referees, each from a different institution and not from the authors' institutions. For direct submission papers, the PNAS Office will invite the referees, secure the reviews, and forward them to the editor. The PNAS Office will also secure any revisions and subsequent reviews. The name of the editor, who may remain anonymous to the author until the paper is accepted, will be published in PNAS as editor of the article. Papers submitted directly are published as “Edited by” the responsible editor and have an additional identifying footnote.

Academy members who have told authors they are willing to oversee the review process have 48 hours from the time of submission to alert the PNAS Office to their request. During this period the PNAS Office will contact the member to confirm. Authors should coordinate submission to ensure the member is available. The Board cannot guarantee that the member will be assigned the manuscript or that it will be sent for review.

An Academy member may “communicate” for others up to 2 manuscripts per year that are within the member's area of expertise. Before submission to PNAS, the member obtains reviews of the paper from at least 2 qualified referees, each from a different institution and not from the authors' or member's institutions. Referees should be asked to evaluate revised manuscripts to ensure that their concerns have been adequately addressed. The names and contact information, including e-mails, of referees who reviewed the paper, along with the reviews and the authors' response, must be included. Reviews must be submitted on the PNAS review form, and the identity of the referees must not be revealed to the authors. The member must include a brief statement endorsing publication in PNAS along with all of the referee reports received for each round of review. Members should follow National Science Foundation (NSF) guidelines to avoid conflict of interest between referees and authors (see Section iii). Members must verify that referees are free of conflicts of interest, or must disclose any conflicts and explain their choice of referees. These papers are published as “Communicated by" the responsible editor.

An Academy member may submit up to 4 of his or her own manuscripts for publication per year. A special obligation applies to a Contributed paper for which the member or coauthors disclose a significant financial or other competing interest in the work. As of January 1, 2009, we will no longer consider such submissions using the contributed route. Members who disclose a significant conflict of interest must submit their manuscripts using standard direct submission. Members must secure the comments of at least 2 qualified referees. Referees should be asked to evaluate revised manuscripts to ensure that their concerns have been adequately addressed. Members' submissions must be accompanied by the names and contact information, including e-mails, of knowledgeable colleagues who reviewed the paper, along with all of the reviews received and the authors' response for each round of review, and a brief statement endorsing publication in PNAS. Reviews must be on the PNAS review form and should not be from the authors' own institution. Members should follow NSF guidelines to avoid conflict of interest between referees and authors (see Section iii). Members must verify that referees are free of conflicts of interest, or must disclose any conflicts and explain their choice of referees. The Academy member must be a corresponding author on the paper. These papers are published as ‘‘Contributed by’’ the responsible editor.

All manuscripts are evaluated by the Editorial Board. The Board may reject manuscripts without further review or may subject manuscripts to review and reject those that do not meet PNAS standards. Manuscripts rejected by one member cannot be resubmitted through another member or as a direct submission. When revisions are requested prior to final decision, revised papers must be received within 2 months or they will be treated as new submissions.

(i) Articles are accepted provided they have not been Published Previously or concurrently submitted for publication elsewhere. Related manuscripts that are in press or submitted elsewhere must be included with your PNAS submission.

Figures or tables that have been published elsewhere must be identified, and permission of the copyright holder for both the print and the online editions of the journal must be provided (see www.pnas.org/site/misc/permissions_letter.pdf).

(ii)Authorship should be limited to those who have contributed substantially to the work. The corresponding author must have obtained permission from all authors for the submission of each version of the paper and for any change in authorship.

All collaborators share some degree of responsibility for any paper they coauthor. Some coauthors have responsibility for the entire paper as an accurate, verifiable report of the research. These include coauthors who are accountable for the integrity of the data reported in the paper, carry out the analysis, write the manuscript, present major findings at conferences, or provide scientific leadership to junior colleagues. Coauthors who make specific, limited contributions to a paper are responsible for their contributions but may have only limited responsibility for other results. While not all coauthors may be familiar with all aspects of the research presented in their paper, all collaborators should have in place an appropriate process for reviewing the accuracy of the reported results.

Authors must indicate their specific contributions to the published work. This information will be published as a footnote to the paper. Examples of designations include:

• Designed research
• Performed research
• Contributed new reagents or analytic tools
• Analyzed data
• Wrote the paper

An author may list more than one contribution, and more than one author may have contributed to the same aspect of the work.

(iii) All authors, members, referees, and editors must disclose any association that poses a Conflict of Interest in connection with the manuscript. Authors must acknowledge all funding sources supporting the work. Editors should follow NSF guidelines to avoid conflict of interest between referees and authors (www.nsf.gov/attachments/108276/public/Conflict_of_Interest_Information.pdf). Recent collaborators, defined as people who have coauthored a paper with the author or member within the past 48 months, should be excluded as referees. Please see www.pnas.org/site/misc/coi.shtml for details.

(iv) Completion of the online submission form electronically gives an exclusive license to publish the work to the National Academy of Sciences. If a paper is declined for publication, the license to publish is terminated.

(v) The Academy may distribute Embargoed copies of an accepted article to the press prior to publication. Embargoes expire at 5:00 p.m. Eastern time on the Monday before publication. Authors may talk freely with the press about their work but should coordinate with the PNAS News Office so that reporters are aware of PNAS policy. If you plan on presenting your embargoed paper at a conference prior to publication, please contact the PNAS News Office immediately at 202-334-1310 or PNASnews{at}nas.edu.

(vi) Research involving Human and Animal Subjects and Clinical Trials must have been approved by the author's institutional review board. Authors must follow the International Committee of Medical Journal Editors' (www.icmje.org) policy and deposit trial information and design into an accepted clinical trial registry before the onset of patient enrollment. Authors must include in the Methods section a brief statement identifying the institutional and/or licensing committee approving the experiments. For experiments involving human subjects, authors must also include a statement confirming that informed consent was obtained from all subjects. All experiments involving human subjects must have been conducted according to the principles expressed in the Declaration of Helsinki.

(vii) For research using Recombinant DNA, physical and biological containment must conform to National Institutes of Health guidelines or those of a corresponding agency.

(viii) Materials and Data Availability. To allow others to replicate and build on work published in PNAS, authors must make materials, data, and associated protocols available to readers. Authors must disclose upon submission of the manuscript any restrictions on the availability of materials or information. Data not shown and personal communications cannot be used to support claims in the work. Authors are encouraged to use Supporting Information to show all necessary data.

Authors must make Unique Materials (e.g., cloned DNAs; antibodies; bacterial, animal, or plant cells; viruses; and computer programs) promptly available on request by qualified researchers for their own use. Failure to comply will preclude future publication in the journal. It is reasonable for authors to charge a modest amount to cover the cost of preparing and shipping the requested material. Contact pnas{at}nas.edu if you have difficulty obtaining materials.

Plasmids: Authors are encouraged to deposit plasmid constructs in a public repository such as Addgene (www.addgene.org).

Databases: Before publication, authors must deposit large data sets (including microarray data, protein or nucleic acid sequences, and atomic coordinates for macromolecular structures) in an approved database and provide an accession number for inclusion in the published paper. When no public repository exists, authors must provide the data as Supporting Information online or, in special circumstances when this is not possible, on the author's institutional Web site, provided that a copy of the data is provided to PNAS.

Characterization of Chemical Compounds: Authors must provide sufficient information to establish the identity of a new compound and its purity. Sufficient experimental details must be included to allow other researchers to reproduce the synthesis. Characterization data and experimental details must be included either in the text or the Supporting Information.

Protein and Nucleic Acid Sequences: Authors must deposit data in a publicly available database such GenBank/EMBL/DNA Data Bank of Japan or Swiss-Prot.

Structural Studies: Authors of papers describing new structure determinations must submit to the Protein Data Bank at the Research Collaboratory for Structural Bioinformatics or its equivalent all structural data required to validate the discussion, including x-ray amplitudes, structure factor files, and the derived atomic coordinates. For nuclear magnetic resonance structures, data deposited should include resonance assignments and all restraints used in structure determination and the derived atomic coordinates for both an individual structure and a family of acceptable structures. Articles must include literature references for all coordinate data sets as well as data set identification. Authors must agree to release the coordinates when the article is published.

Functional Magnetic Resonance Imaging (fMRI) Studies: Authors should deposit data with the fMRI Data Center or other suitable public repositories.

Genomic and Proteomic Studies: Authors of papers that include genomic, proteomic, or other high-throughput data are required to submit their data to the NCBI gene expression and hybridization array data repository (GEO, www.ncbi.nlm.nih.gov/geo) or equivalent publicly accessible database and must provide the accession number. Access to the information in the database must be available at the time of publication. Submitted data should follow the MIAME checklist (for more information, see www.mged.org/Workgroups/MIAME/miame_checklist.html).

(ix) Figure Preparation. No specific feature within an image may be enhanced, obscured, moved, removed, or introduced. The grouping or consolidation of images from multiple sources must be made explicit by the arrangement of the figure and in the figure legend. Adjustments of brightness, contrast, or color balance are acceptable if they are applied to the whole image and if they do not obscure, eliminate, or misrepresent any information present in the original, including backgrounds. Questions about images raised during image screening will be referred to the editors, who may request the original data from the authors for comparison with the prepared figures. If the original data cannot be produced, the manuscript may be rejected. Cases of deliberate misrepresentation of data will result in rejection of the paper and will be reported to the corresponding author's home institution or funding agency.

(x) Supporting Information (SI): SI enhances papers in PNAS by providing additional substantive material, but the print version of the paper must stand on its own merits. SI is reviewed along with the paper and must be approved by the editors and referees. Instead of appearing in the printed version of the journal, SI is posted on the PNAS Web site at the time of publication. SI is referred to in the text and cannot be altered by authors after acceptance. Data not shown and personal communications cannot be used to support claims in the work. Authors are encouraged to use SI to show all necessary data.

SI may take the form of supplemental figures, tables, datasets, derivations, and videos. Authors should express in their cover letter their intention to include SI with their paper. In addition, editors may suggest that part of the submitted data could be more suitably presented online only to save journal space and to focus the article.

(xi) PNAS Early Edition. PNAS articles are published daily online before print at www.pnas.org in PNAS Early Edition. Papers may be published online 1 to 4 weeks before they appear in print. Authors who return proofs quickly and keep changes to a minimum get maximum publication speed. The EE publication date is the official date of record.

(xii) Errata: PNAS publishes corrections for errors, made by the journal or authors, of a scientific nature that do not alter the overall basic results or conclusions of a published article. PNAS publishes retractions for major errors that may call into question the source of the data or the validity of the results and conclusions of an article. Errata are published at the discretion of the editors and appear as formal printed and online notices in the journal.

Contact Information

PNAS, 700 11th Street, NW, Suite 450, Washington, DC 20001. Phone 1-202-334-2679, fax 1-202-334-2739, e-mail pnas{at}nas.edu.

Courier or express mail: PNAS, 700 11th Street, NW, Suite 450, Washington, DC 20001 USA.

Page charges
PNAS depends, in part, on the payment of page charges for its operation. Payment of the page charge of $70 per printed page will be assessed from all authors who have funds available for that purpose. Authors will be charged for extensive alterations on proofs and for submission of revised files after the article is transmitted to the printer. Payment of $250 per article will be assessed for SI. Authors of research articles may pay a surcharge of $1,200 to make their paper freely available through the PNAS open access option. If your institution has a Site License, the open access surcharge is $850. All articles are free online after 6 months. Articles are accepted or rejected for publication and published solely on the basis of merit.

Color charges
Payment by authors of the following additional costs is expected: $300 for each color figure or table; an additional $150 for each replacement or deletion of a color figure or table. A single figure is defined as original art that can be processed as a unit and printed on 1 page without intervening type. Requests for waiver of charges should be submitted to pnas{at}nas.edu.

Prior to submission, authors who believe their manuscripts would benefit from professional editing are encouraged to use a language-editing service (see list at http://www.pnas.org/site/misc/language-editing.shtml). PNAS does not take responsibility for or endorse these services, and their use has no bearing on acceptance of a manuscript for publication.

Authors must submit their articles at www.PNAScentral.org. A surcharge of $50 will be assessed for all hardcopy submissions. Source files are required for all submissions, including revisions. Members communicating or contributing papers should also submit via the Web. Corresponding authors of communicated and contributed papers will be provided a URL for file submission after the member has initiated the process by providing his or her endorsement and copies of the reviews received. SI must also be submitted online.

Only TIFF and EPS, and high-resolution PDF for Mac or PC are allowed for figures that will appear in the print journal. (See Supporting Information below for acceptable formats for online-only material.) Color images must be in RGB (red, green, blue) mode. Include the font files for any text. PC or Mac versions of Adobe PostScript fonts must be used (no system "bitmap" fonts). Images must be final size, preferably 1 column width (8.7 cm). Figures wider than 1 column should be between 10.5 and 18.0 cm wide. Numbers, letters, and symbols should be no smaller than 6 points (2 mm) and no larger than 12 points (6 mm) after reduction and must be consistent. Composite figures must be preassembled. Figures must be submitted as separate files, not embedded in manuscript text. See www.pnas.org/site/misc/digitalart.pdf or contact pnasdigart{at}cadmus.com.

Each table should have a brief title, be on a separate page, and be double-spaced. Tables must be submitted as separate files, not embedded in the manuscript text.

The print version of the paper must stand on its own without the SI. Refer to SI in the manuscript at an appropriate point in the text. Number supporting figures and tables starting with S1, S2, etc. Authors are limited to no more than 10 SI files, not including movie files.

Authors who place detailed materials and methods in SI must provide sufficient detail in the print edition methods to enable a reader to follow the logic of the procedures and results and also must reference the online methods. If a paper is fundamentally a study of a new method or technique, then the methods must be described completely in the print edition.

Because PNAS edits SI and composes it into a single PDF, authors must provide the following file formats only:

• Text: Supply Word, WordPerfect, RTF, or LaTeX files (LaTeX files must be accompanied by a PDF with the same file name for visual reference).
  
• Figures: Provide a brief legend for each figure in a Word, WordPerfect, or RTF file. Provide figure images in TIFF, EPS, high-resolution PDF, JPEG, or GIF format; figures may not be embedded in manuscript text. Do not save figure numbers, legends, or author names as part of the image. Composite figures must be preassembled. Images should not exceed 500 pixels per inch in width or height.
  
• Tables: Supply Word, WordPerfect, RTF, or LaTeX files (LaTeX files must be accompanied by a PDF with the same file name for visual reference); include only 1 table per file. Do not use tabs or spaces to separate columns in Word or WordPerfect tables.
  
• Movies: Supply Audio Video Interleave (avi), Ouicktime (mov), Widows Media (wmv), Animated GIF (gif), or MPEG files and submit a brief legend for each movie in a Word, WordPerfect, or RTF file. All movies should be submitted at the desired reproduction size and length. Movies should be no more than 10 MB in size.
  
• Still images: Authors must provide a still image from each video file. Supply TIFF, EPS, high-resolution PDF, or JPEG files.

As a publisher, PNAS must be able to archive the data essential to a published article. Where such archiving is not possible, deposition of data in public databases, such as GenBank, ArrayExpress, Protein Data Bank, Unidata, and others outlined in the Information for Authors, is acceptable.

Only links to Web sites that are permanent public repositories, such as self-perpetuating online resources funded by government, academia, and industry, are permitted. Links to an author's personal Web page are not acceptable. PNAS allows authors to post their PNAS paper on their home page after the paper is published in PNAS.

Authors are invited to submit scientifically interesting and visually arresting cover images. To view examples of cover art, see www.pnas.org/coverarchive. Illustrations need not be reprinted in the article but should be representative of the work. Images should be original, and authors grant PNAS the exclusive license to publish. Include a brief lay-language caption (50-60 words) and credit information (e.g., Photograph courtesy of...). Images should be 21.5 cm wide by 22.5 cm high. Files should be EPS or TIFF and should be in CMYK (cyan, magenta, yellow, black) color mode. Cover figure files may be submitted online when the paper is submitted or may be sent by e-mail to PNASCovers{at}nas.edu. Send large files on CD-ROM by courier to the PNAS Office or contact PNAS for FTP instructions. Submissions provided outside the online submission system should include manuscript number, author name, phone, and e-mail. Illustrations will not be returned unless requested.

PNAS generally uses a 2-column format averaging 67 characters, including spaces, per line. The maximum length of a research article is 6 printed pages, including all text, spaces, and the number of characters displaced by figures, tables, and equations.

An online submission tool provides authors with an estimation of whether their manuscript fits within the PNAS length requirements (see Length Estimate FAQ). Use the following guidelines to determine whether your manuscript exceeds the page-length requirements pre-submission:

• Text: When submitting tables, figures, and/or equations in addition to text, you should keep the text for your manuscript under 39,000 characters (including spaces).
• Figures: Calculated at 180 characters per cm in height for 1 column and 360 characters per cm in height for 2 columns; a figure wider than 8.7 cm takes up 2 printed columns in width.
• Tables and equations: Calculated at 60 characters per line for 1 column and 120 per line for 2 columns; a table with more than 60 characters per line will take up 2 printed columns in width.

Authors will be responsible for additional charges incurred due to shortening overlong papers in proof.

The standard order of sections in the manuscript file is: title page, abstract, introduction, results, discussion, materials and methods, acknowledgments, references, figure legends, and table legends. Number all manuscript pages starting with the title page as page 1. Figures and tables are uploaded separately from the manuscript.

Title Page. Include the following information on this page:

• Classification: Select a major (Physical, Social, or Biological Sciences) and a minor category from the following. Dual classifications are permitted between major categories and in exceptional cases, subject to Editorial Board approval, within a major category.
  
  
  • PHYSICAL SCIENCES: Applied Mathematics, Applied Physical Sciences, Astronomy, Chemistry, Computer Sciences, Engineering, Environmental Sciences, Geology, Geophysics, Mathematics, Physics, Statistics, and Sustainability Science.
    
    
  • SOCIAL SCIENCES: Anthropology, Economic Sciences, Environmental Sciences, Political Sciences, Psychology, Social Sciences, and Sustainability Science.
    
    
  • BIOLOGICAL SCIENCES: Agricultural Sciences, Anthropology, Applied Biological Sciences, Biochemistry, Biophysics and Computational Biology, Cell Biology, Developmental Biology, Ecology, Environmental Sciences, Evolution, Genetics, Immunology, Medical Sciences, Microbiology, Neuroscience, Pharmacology, Physiology, Plant Biology, Population Biology, Psychology, Sustainability Science, and Systems Biology.
    
    
• Title: Titles should be no more than 3 typeset lines (generally 135 characters including spaces) and should be comprehensible for a broad scientific audience.
• Author affiliation: Include department, institution, and complete address, with the ZIP/postal code, for each author. Use superscripts to match authors with institutions.
• Corresponding author: The name, complete address, telephone and fax numbers, and e-mail address of the author to whom correspondence and proofs should be sent. Mailing and e-mail addresses will appear in print and online.
• Manuscript information: The number of text pages (including references and figure legends), of figures, and of tables.
• Abbreviations: Define nonstandard abbreviations where first mentioned in text.
• Data deposition footnote: Supply all database accession numbers and/or codes.

Abstract. Provide an abstract of no more than 250 words on page 2 of the manuscript. Abstracts should explain to the general reader the major contributions of the article. References in the abstract must be cited in full within the abstract itself and cited in the text.
 
Text. Describe procedures in sufficient detail so that the work can be repeated. Methods must be presented after Results and Discussion. Follow the spelling and usage given in Webster's Third New International Dictionary or the Random House Dictionary of the English Language. Avoid laboratory jargon. Correct chemical names should be given, and strains of organisms should be specified. Trade names should be identified by an initial capital letter with the remainder of the name lowercase. Names of suppliers of uncommon reagents or instruments should be provided. Use Système International (SI) units and symbols whenever possible.  

Footnotes. PNAS now distinguishes author affiliations and footnotes from in-text footnotes by assigning a different set of footnote symbols to each type. Superscript lowercase letters separated by commas (no spaces) are used for author affiliations. Superscript numerals separated by commas (no spaces) are used for author footnotes. In-text footnotes should be preceded by a footnote symbol, used in the order *, , , §, ¶, , **, , , §§, ¶¶.
 
Acknowledgments. List acknowledgments and funding sources. Dedications are rarely allowed.
 
References. References must be in PNAS style. Only published or in-press papers and books may be cited in the reference list. Unpublished abstracts of papers presented at meetings or references to "data not shown" are not permitted. References should be cited in numerical order as they appear in text. Because tables and figures will be inserted in the text where first cited, references in these sections should be numbered accordingly. Include the full title for each cited article. Authors must translate foreign language titles into English, with a notation of the original language. All authors (unless there are more than 5) should be named in the citation. If there are more than 5, list the first author's name followed by et al. Provide inclusive page ranges for journal articles and book chapters. Cite databases in the text or as footnotes.

The corresponding author must be prepared to provide a signed authorization for the citation of personal communications.
 
Journal articles are cited as follows:
 
10.  Neuhaus J-M, Sitcher L, Meins F, Jr, Boller T (1991) A short C-terminal
       sequence is necessary and sufficient for the targeting of chitinases
       to the plant vacuole. Proc Natl Acad Sci USA 88:10362-10366.
 
For correct abbreviations of journal titles, refer to Chemical Abstracts Service Source Index (CASSI).

Articles or chapters in books are cited as follows:
 
14.   Hill AVS (1991) in Molecular Evolution of the Major Histocompatibility
       Complex, eds Klein J, Klein D (Springer, Heidelberg), pp 403-420.
 
Figure Legends. Provide these separately from figures, after the references in the manuscript. For figures with multiple panels, the first sentence of the legend should be a brief overview of the entire figure. Graphs should include clearly labeled error bars described in the figure legend. Authors must state whether a number that follows the ± sign is a standard error (s.e.m.) or a standard deviation (s.d.). The number of independent data points (N) represented in a graph must be indicated in the legend. Numerical axes on graphs should go to 0, except for log axes. Statistical analyses should be done on all available data and not just on data from a “representative experiment.” Statistics and error bars should only be shown for independent experiments and not for replicates within a single experiment.

Use international standards on nomenclature. For approved abbreviations and symbols, see www.pnas.org/site/misc/iforc.shtml#abbreviations. PNAS uses Scientific Style and Format: The CSE manual for authors, editors, and publishers (7th edition, 2006) as the primary guide for journal style.

Table 1. Standard Abbreviations and Symbols
Table 2. Abbreviations for units of measurement and physical and chemical quantities