Ratio of acrylamide to bis-acrylamide - different percentages for DNA and protein gels (Nov/19/2007 )

hi all,
I am confused abt what should be the ratio of acylamide and biacrylamide for PAGE gels for western blot and DNA gels.I have found a number of ratios :19:1,29:1,37.5:1 and 49:1.How do i choose an ideal combination for both purposes? Or should i make different percentages.Colleagues in my lab weigh 45gms of acrylamide and 1.68 gms of bis.This has been a standard practice.
Any suggestions in this regard will be very helpful.
Thanks,
Nirupa

you should use different ratios for different purposes.

in general:

37.5:1 is nearly universal for protein electrophoresis.

29:1 is used for nucleic acid separation other than sequencing.

19:1 is used for sequencing nucleic acids.