Upper limit of MgCl2 in PCR

Dr. Peter Gegenheimer PGegen at kuhub.cc.ukans.edu
Fri Jun 13 18:47:13 EST 1997


In <tyou.59.339E5478 at postbox.acs.ohio-state.edu>, tyou at postbox.acs.ohio-state.edu (Taek H. You) writes:
>
>>Ng Hian Cheong (medp3019 at leonis.nus.sg) wrote:
>
>>What is the reason for the existence of an upper limit of MgCl2 
>>concentration during PCRs ?? What is this value, 10 mm or 15 mM ?
///// snip /////
>primers can anneal more stably (in a sense, to nonspecific sites too). More 
>importantly, Mg++ binds to nucleotides. Polymerization requires free 
>nucleotides, not Mg++-bound nucleotides to synthesize. This can be overcome 
>with higher nucleotide concentration.

All nucleotide polymerizing enzymes (at least those which use triphosphates) -- indeed, most nucleotide-utilizing enzymes -- use the Mg-nucleotide chelate. Mg is usually chelated by the oxygens of the beta and gamma phosphates. 

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