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magnesium in pcr - what does it do?

Dima Klenchin klenchin at macc.wisc.edu
Tue Dec 5 16:43:36 EST 1995


In article <k9mhc.131.005C5B48 at rfhsm.ac.uk>, k9mhc at rfhsm.ac.uk (vid mohan-ram) 
wrote:
>what is it that mg actually does in the mix?......make dna more accesible to 
>polymerase or what?.......and whats the relationship between mg and dntp 
>concentrations?

AFAIR, _all_ enzymatic reactions involving trinucleotides are Mg (other
metals could substitute with efficiency that varies) dependent due to simple
reason: the substrate is Mg-NTP complex. 

Affinity of divalent Me for NTPs is around 0.2-2 mM (depends) so at 2 mM Mg 
practically all amount of NTPs added is a substrate. 

In PCR, I'd say, DNA interactions, melting temp., etc are secondary 
factors that come to play. 



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