Need help with pre run of PAGE. - (May/29/2011 )

Hi there,

I am performing a Urea - PAGE for size separation of products of 112 - 300 bp dna range, Just cant understand the usefulness of pre - run in the whole procedure & how it is done ? Did we have to first load the ONLY loading dye in the wells & then allow the pre run @ say 80 W for an hour OR we just as such pre run the gel to heat it up ? I performed Urea PAGE once with a pre- run , my bands were bowed or V shaped ? does this is because of less time of pre run or the dis-continuation of the pre run that happens due to power failure ?
my general protocol says pre run at 80 W for an hour atleast & then run at 1 & 1/2 hour for size separation .

Pls guide me a little bit for this procedure

Thanks.

we pre-run to heat the gel.