Nucleic Acids Research, Vol 25, Issue 4 800-805, Copyright © 1997 by Oxford University Press
MC Raja, D Zevin-Sonkin, J Shwartzburd, TA Rozovskaya, IA Sobolev, O Chertkov, V Ramanathan, L Lvovsky and LE Ulanovsky
Here we describe template directed enzymatic synthesis of unique primers,
avoiding the chemical synthesis step in primer walking. We have termed this
conceptually new technique DENS (differential extension with nucleotide
subsets). DENS works by selectively extending a short primer, making it a
long one at the intended site only. The procedure starts with a limited
initial extension of the primer (at 20- 30 degrees C) in the presence of
only two out of the four possible dNTPs. The primer is extended by 6-9
bases or longer at the intended priming site, which is deliberately
selected, (as is the two-dNTP set), to maximize the extension length. The
subsequent termination reaction at 60-65 degrees C then accepts the
extended primer at the intended site, but not at alternative sites, where
the initial extension (if any) is generally much shorter. DENS allows the
use of primers as long as 8mers (degenerate in two positions) which prime
much more strongly than modular primers involving 5-7mers and which (unlike
the latter) can be used with thermostable polymerases, thus allowing cycle-
sequencing with dye-terminators compatible with Taq DNA polymerase, as well
as making double-stranded DNA sequencing more robust.
ARTICLES
DNA sequencing using differential extension with nucleotide subsets (DENS)
Center for Mechanistic Biology and Biotechnology, Argonne National Laboratory IL 60439-4833, USA.
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