how leaky is it for lacIq?

benedik at benedik at
Mon Jul 10 17:38:06 EST 1995

In article <3trs2e$e5d at>
ingnang at (Ing nang) writes:

> Hi,
> I wonder if any one can give me some clues on this, so I won't loose 
> any sleep tonight :).    If you have two copies of lac promotors on the
> plasmid, say, pBlueScript, and the host cell has lacIq mutation on it, how
> tightly controlled the expression would be?  Could the over-produced lac
> repressors be diluted by the presence of two promotors, so that the 
> expression becomes leaky?
> --
> Ing-Nang Wang
> Dept. Ecology and Evolution
> SUNY-Stony Brook
> ingnang at

quite leaky. Assuming a high copy number plasmid like pUC18 or
pBluescript, the lacIq allele in most cloning strains will only
partially regulate the promoter. You require IPTG for full induction,
but it definately is quite on without inducer. You need a plasmid
encoded lacI gene to really repress such high copy number plasmids.

Michael Benedik               benedik at
Biochemical Sciences
University of Houston
Houston, TX 77204-5934

More information about the Methods mailing list