I have been sequencing short to medium lenght PCR products successfully
(on a 377 ABI) up until a few weeks ago. I use shrimp alkaline
phosphatase and exonuclease I as a cleanup.
Recently all PCR sequencing has come to a halt. I get only short blips
on the gel image. As well, the controls have much higher background,
and more N's than normal.
I have tried increasing the DNA and ethanol precipitation of the DNA to
remove the inactive enzymes, to no avail.
Has anyone else had this problem?
Are there any suggestions?