Magnesium effects on PCR

[RAY-Francois Comte]

On 5 Feb 1996, Dubear Kroening wrote:

> Date: 5 FEB 1996 19:03:02 GMT 
> From: Dubear Kroening <dubear at offroad>
> Newgroups: bionet.molbio.methds-reagnts
> Subject: Magnesium effects on PCR 
> 
> 
> Hello,
> 
> Does anyone know of any detailed studies on the effects of magnesium 
> on PCR?  I've searched the web, PCR books, and medline but cannot find 
> enough info.  For instance, what exactly Mg does, what concentrations 
> are better for certain size products and why they vary, whether there 
> is a range one can use if trying to amplify different size products, 
> etc...   Any info would be greatly appreciated.
> 
> Dubear Kroening
> dubear at whitewater.chem.wisc.edu
> 
> 
>I don't have any books or references to suggest but I heard that Mg is 
essential for the polymerase. Also, it is said that the annealing of the 
primers to the template is influence by the salt concentration (MgCl2 can 
be considered as a salt). I recently tried to amplify a small fragment 
and found that the Mg had a BIG influence in my conditions. Usually there 
is 1,5 mM of Mg in a PCR reaction, I tried 0,75 mM and 3 mM and observed 
that there is an optimum that can be obtained between high specificity and 
low yield (high Mg) and low specificity and high amplification (low Mg). 

I hope this will help you in some way.

Francois