Appeal No. 95-3606
Application 07/827,691
the PCR process and interfere with normal gel migrations
(Innis I,
col. 3, l. 44-58). The problem Innis I confronts is most
prevalent in nucleic acid sequences having high guanosine (G)
and cytosine (C) content, i.e., sequences most likely to form
Hoogsteen bonds (Innis I, col. 3, l. 51-54). Innis I proffers
the following solution (Innis I, col. 4, l. 22-43):
The utilization of c dGTP [(7-deaza-2'-7
deoxyguanosine-
5'-triphosphate)] in a polymerase chain reaction results
in
the incorporation of 7-deazaguanine into the amplified
DNA
produced in the reaction. . . . 7-deazaguanine precludes
Hoogsteen bond formation . . . [and] does not impair
Watson-
Crick base pairing as does inosine, another structure-
destabilizing base analog. Utilization of inosine in PCR
results in frequent mismatching of bases during primer
extension.
Utilization of c dGTP in PCR, however, results in an7
astounding increase in the specificity of PCR on nucleic
acid templates that contain secondary structure and/or
compressed regions.
Moreover, Innis I prefers to use c dGTP in combination with7
dGTP in the PCR reaction mixture for greatest efficiency
(Innis I, col. 4, l. 38-43):
PCR reactions performed with c dGTP but without dGTP are7
typically less efficient than PCR reaction performed
with mixtures of c dGTP and dGTP. The optimum mixture7
is believed to be about 3:1 c dGTP and dGTP, respectively.7
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