lacI Repressor in domesticated Coli

[Andreas "Mega" Stuermer]

Hi guys, 

I was wondering if it is neccessary to express the lac repressor protein in DH5a and similar strains to be able to use the lac or tac promoter, or if this one is still intact in coli? 

Google is remarkably unhelpful. 

I would think it is still intact? 

[Matt Lawes]

Yes the endogenous lacI repressive is there so. I need to add another. You add inducer IPTG to control gene expression from the lac promoter ....the inducer causes the repressor  to fall off  the lacO operator that overlaps the lac promoter. Now RNA Polymerase can come in and transcribe from lac promoter ..... the more IPTG the more expression you get .. kind of linear (sigmoidal with a large linear center).

>matt

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[Matt Lawes]

Edit .. typo. ... "endogenous lacI represssor is there so no need to add another" is what it should read.

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[Andreas "Mega" Stuermer]

Sweet, thanks so much for your insight! That's great news