Direct selection for GalE in E.coli

Rafael Maldonado rafael at
Mon Mar 20 14:07:45 EST 1995

On Mon, 20 Mar 1995, Duncan Clark wrote:
> Why do I want a GalE delta(lac-proAB) host? If you use pUC18 in such 
> a host with IPTG/Xgal etc the alpha complementation is lethal with
> phenylgalactoside. This gives a direct selection for whites. Just 
> think, no phosphatasing and everything has an insert.

HA! You're not the first one in thinking of that.

Gossen et al. (1992) Application of galactose-sensitive E. coli strains as 
selective hosts for LacZ- plasmids. NAR 20, 3254.

I think that you can get some other mutation that mimics the toxicity of 
galactose, but I think happens at very low frequency. Others mutations 
may be in the lacZ of your plasmid.

Why are not people using this system? You know, MBist are too lazy to 
change techniques... and the X-gal system works pretty well.



Rafael Maldonado			"You gave to a boy the job  
Department of Human Genetics		 of a man. He's dead."
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