Zhixiang Hu xiang at
Fri Dec 9 14:55:50 EST 1994

In article <stauth-081294142709 at>,
stauth at (Darren Stauth) wrote:

> We recently started making competent cells using DMSO and PEG3350 and we
> were excited at its ease and efficiency.  We are using DH5-alpha cells and
> transforming TA ligations.  However, we are now running into the problem of
> cell lawns appearing on our transformation plates containing amp.  First
> the transformants appear and then a few hours later the lawn becomes
> visible.  We have tested the amp and the cells both are fine.  Is the
> treating of the cells to make them competent somehow causing them to be
> resistant to amp?  Has anybody experienced this problem?   Any suggestions
> welcome.

I have a simlilar problem with electroplation. We do get seperate
transformants on the plate. However, only one out of ten clones can grow
in liquid media or new plates. The cells are DH12. Plasmids are pBR322
derivatives. One of my colleagues has the same problem with BL21(DE3) and
pET vectors.
Does anybody have a sound explaination?

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