IPTG induction in non E.coli strains

Aawara Chowdhury via methods%40net.bio.net (by aawara from FEMA-trailer.org)
Tue Mar 20 07:25:12 EST 2007

In <S1PLh.13817$8U4.11415 from news-server.bigpond.net.au>,
 newsnet customer <customer from newsnet.com> 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.
> lacI repressor protein binds to the lac operator and NOT the lac operon.

Since when did the lac operator stop being in the lac operon?  And certainly
describing lacI to bind the lac operon is considerably more accurate than
your original description, "IPTG binds to the lac z operon .....".

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