Taq - not so promiscuous???

Robert Horton horton at molbio.cbs.umn.edu
Tue Dec 15 16:03:13 EST 1992

	Your observation of a low rate of incorporation of errors by Taq
is not unusual. We found no errors in over 6000 bases from clones amplified
from cDNAs (J. Immunol. 145:1782-7, 1990). The reaction conditions were
"standard" except that the [Mg++] was a little low (1mM). We had slightly
higher error frequencies in other experiments, which happened to use slightly
more Mg. (dNTPs were always 200uM each).
	I think Taq often gets a bum rap as far as errors introduced into
clones is concerned. The key may be that error _frequency_ (i.e., the
observed fraction of errors incorporated into the product) is not directly
correlated with error _rate_ (the fraction of wrong bases incorporated
by Taq). This is because of "thermal proofreading" (as I believe they call
it in California), in which DNA strands that get the wrong base added don't
get extended efficiently by polymerase, so these errors don't show up in
the final product.

Bob Horton            /\ "Crash programs fail because of the theory that
U. of Minnesota, CBS  || with nine women pregnant you get a baby a month" 
1479 Gortner Ave.    /||\   -Werner von Braun.  Disclaimer:"Bob who?"
St. Paul, MN 55108    ^^   horton at molbio.cbs.umn.edu/(612) 624-3790

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