magnesium in pcr - what does it do?

[vid mohan-ram]

hi,....

title says it all really.....i know dntps, dna and proteins all bind mg but 
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?

thanks

vid
k9mhc at rfhsm.ac.uk