IPTG induction in non E.coli strains

[Kyle Legate]

newsnet customer wrote:
>>> IPTG binds to lac repressor coded from lacI, but pUC18 doesn't carry any 
>>> lacI gene, so I suppose that lacI is coded from the host strains. Does it?
> 
> IPTG binds to the lac z operon to induce the lac z gene to express 
> beta-galactosidase. beta-galactosidase hydrolyses colorless X-gal to produce 
> insoluble blue preciptate (blue colonies). pUC18 does not have lacI gene as 
> this would inhibit the expression of beta-galactosidase, therefore blue 
> white screening would be impossible.
> 

Oh dear. It's a good thing for you you're anonymous. As you should have 
learned in introductory biochemistry, lacI binds to the lac operon 
(lacO), preventing transcription of LacZ-Y-A. IPTG binds lacI, which is 
then released from lacO to permit transcription.