Hi,
This could be a detergent front. One way around it it to keep running
the gel for 30min-1hr after the dye runs off.
Alternatively old anode buffer causes precipitation at the bottom of the
gel which sometimes can actually be seen without staining.
A friend of mine investigated this phenomenon and came to several conclusions:
you can contact him on rbarry at proteome.org.au
--
Paul Cullen
Bacterial Pathogenesis Research Group
Monash University
Australia
