[Paleopsych] DNA with three base pairs - A step towards expanding the genetic code
shovland at mindspring.com
Tue Mar 15 22:56:54 UTC 2005
SAN DIEGO, March 14, 2005 --Scientists at The Scripps Research Institute in
La Jolla, California are reporting today at the 229th national meeting of
the American Chemical Society progress toward the creation of a system for
replicating a modified form of DNA containing an unnatural base pair.
According to the Scripps Research scientists, this finding is a significant
step towards expanding the genetic code and the ability of DNA to act as an
information storage and retrieval system in the test tube and in simple,
engineered organisms, such as yeast or bacteria. DNA with three or more
base pairs could find broad applications in a number of fields, including
biotechnology, medicine, data storage, and security.
Instead of just the canonical base pairs "G-C" or guanine-cytosine, and
"A-T" or adenine-thymine, the Scripps Research scientists' DNA has a third
pairing: "3FB-3FB" between two unnatural bases called 3-fluorobenzene (or
3FB). Unlike other unnatural base pairs, DNA polymerases are able to
replicate this base pair, albeit with reduced fidelity. To improve
replication, the scientists also reported the development of a system
capable of evolving polymerases to better recognize 3FB in DNA. Using a
selection system some liken to evolution in the test tube, they are
creating their own "polymerase" enzyme able to replicate the unnatural DNA.
While the polymerase does not replicate the unnatural DNA with the same
fidelity observed in nature, (roughly one mistake for every 10 million
bases of DNA copied), its fidelity is reasonable (typically making only one
mistake for every1000 base pairs). This is the first time anyone has been
able to replicate unnatural DNA with fidelity against every possible
"We definitely are still working on improvements, especially in fidelity,"
says Scripps Research Assistant Professor Floyd Romesberg, who led the
research. "Nevertheless, we are now able to replicate unnatural DNA."
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