Upper limit of MgCl2 in PCR

Ned Mantei mantei at neuro.biol.nospam.ethz.ch
Tue Jun 10 09:02:39 EST 1997

In article <5nit5k$3rh at nuscc.nus.sg>, medp3019 at leonis.nus.sg (Ng Hian
Cheong) wrote:

> 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 ?
> I have experience this "upper limit of MgCl2 conc. in PCRs b4:

Magnesium stabilises double-stranded DNA, much more so on a molar basis
than monovalent cations. Perhaps (1) the double-stranded product wasn't
melting any more, or (2) had so much secondary structure at the
hybridization temperature that primers couldn't anneal, or (3) had
sufficient structure at the synthesis temperature that the polymerase
couldn't work.

Ned Mantei
Dept. of Neurobiology, Swiss Federal Institute of Technology
CH-8093 Zurich, Switzerland
mantei at neuro.biol.ethz.ch   Fax: +41-1-633-1046

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