[Paleopsych] DNA with three base pairs - A step towards expanding the genetic code

[Steve Hovland]

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 
mispair.
"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."

http://www.eurekalert.org/pub_releases/2005-03/acs-wt030805.php