Blue Colony?

[Paul N Hengen]

ddsyr at NS.EAST.CN.NET wrote:

> Recently I tansformed the pGEM-3Z plasmid vector (from Promega) into E. coli
> DH5a and spreaded on LB plate containing amp 100 ug/ml, X-Gal 20 ul (4% )and 8
> ul IPTG(2%). After 37C overnight, I found the some colonys on plate are blue,
> but more than half of them are white. Since I only used the vector, this
> phenomeno should not happen. Can anynoe give me suggestion? Thanks in advance.

I assume you bought the plasmid DNA directly from Promega, and the competent
cells from some other company, right? Did you do mini-preps of the white
colonies to see if they have inserts? That would be an important thing to find
out. Are they all the same size?  If so, you should determine which is the
problem, the cells or the plasmid DNA, and then give the company the isolated
plasmid DNA with insert so they can screen their lots for the contaminant.
If you find out, please post here warning others about it.

--
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* Paul N. Hengen, Ph.D.                           /--------------------------/*
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