![Models of the structure of T7 DNA polymerase bound to a DNA substrate molecule.](images/79a.jpg) |
![Models of the structure of T7 DNA polymerase bound to a DNA substrate molecule.](images/79b.jpg) |
Models
of the structure of T7 DNA polymerase
bound to a DNA substrate molecule. |
The international effort to decode
the human genome is ahead of schedule,
thanks in part to new tools that have
accelerated DNA sequencing and reduced
its cost. (The DOE sequencing team
can generate more data in 8 days now
than it did in all of 1998, its first
full year of operation.) One such
tool developed in the mid-1990s is
an enzyme, a type of DNA polymerase.
Polymerases, which in their natural
form help cells replicate genetic
material, are used in sequencing to
incorporate fluorescent tags into
DNA to identify the locations of specific
chemical units. Naturally occurring
polymerases tend to reject fluorescent
labels. But Stanley Tabor and Charles
Richardson of Harvard Medical School,
with Office of Science support, applied
fundamental discoveries of the structure
and mechanisms of polymerases to create
a new DNA polymerase, in which a single
chemical change eliminated the bias
against fluorescent basesthereby
producing more usable data than was
generated previously. This discovery,
along with other new knowledge about
organisms living in extreme environments,
was used by a company to engineer
a polymerase that both incorporates
the labels and has the thermostability
needed for sequencing.
Scientific Impact:
Tabor and Richardson's discovery solved
a long-standing problem in genetic
research. The commercial enzyme, ThermoSequenase,
now used by all DNA sequencing centers,
has improved the quality of sequencing
data and reduced the costs.
Social Impact: ThermoSequenase
has captured a very large share of
the DNA-polymerase world market, now
more than $350 million and growing.
It is among the tools used in decoding
the human genome, recently completed
in "working draft" form, which is
expected to lead to new understanding
of, and treatments for, human diseases.
Reference: Tabor,
S., and Richardson, C. C. (1995) "A
single residue in DNA polymerases
of the Escherichia coli DNA polymerase
I family is critical for distinguishing
between deoxy- and dideoxyribonucleotides,"
Proc. Natl. Acad. Sci. USA
92, 6339-6343.
Doublié, S., Tabor, S., Long, A. M.,
Richardson, C. C. and Ellenberger,
T. (1998) "Crystal structure of a
bacteriophage T7 DNA replication complex
at 2.2 Ã… resolution," Nature
39, 251-258.
Patents: Tabor, S.,
and Richardson, C. C. (1997) DNA polymerases
with a modified nucleotide binding
site for DNA sequencing. U. S. patent
number 5,614,365.
Tabor, S., and Richardson, C. C. (1997)
Method of sequencing based on uniform
band intensities. U. S. patent number
5,674,716.
URL:
http://sbweb.med.harvard.edu/~bcmp/html/faculty/richardson.shtml
Technical Contact:
Dr. Marvin Stodolsky, Life Sciences
Division, Office of Biological and
Environmental Research, 301-903-4742
Press Contact: Jeff
Sherwood, DOE Office of Public Affairs,
202-586-5806
SC-Funding Office:
Office of Biological and Environmental
Research |