James Abbott at
Wed Dec 2 16:01:53 EST 1998

Tsunehisa Namba wrote:
>    I need to PCR GC rich sequence.  So far, I tried  various denaturing/
> annealing temp without success.  I would like to try DMSO.
>    Could anyone tell me the concentration of DMSO and other cautions for PCR?

Hi Tsunehisa,

DMSO can usually give results in GC-rich regions when used at a final
concentration of 5%, although there are reports in the literature of
genes which required 10% DMSO, so a bit of experimentation may be
necessary to optimise the concentration for your genes. Alternatively,
addition of Betaine to concentrations of 1M in reactions can also be
beneficial in GC-rich regions. 

There was a comparison published in Promega Notes 65 p 27-29 where the
effectiveness of betaine and DMSO, used separately and together in
reactions, where compared to commercially available PCR additives, along
with NMR spectra confirming that some of these expensive additives are
little more than betaine! In this study, the use of 5% DMSO alone
produced a number of non-specific bands, and a strong specific band,
while 1M betaine used alone resulted in the specific band alone, but
probably about half the amount of product. Combining DMSO and betaine
together in the reaction resulted in the single specific band, but
perhaps in slightly greater proportions than when using betaine alone.

Hope this is of some use,

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