Unusual manual sequencing problem

[Ian Gordon Goodfellow]

Hi,
I saw similar effects myself a year or so ago - turned out it was the
labelling mix contaminated with ddntp - some undergraduate had done
it! Could the same be happening here?
Have you tried new lab mix / ddntp's? It may be that you're lab mix has
been contaminated with ddGTP - which would explain why it is the G bands
and why it fades with longer runs.

Hope this is of some help

Ian Goodfellow