IPTG induction in non E.coli strains

[newsnet customer]

>>>> 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.

lacI repressor protein binds to the lac operator and NOT the lac operon.

ST