Fold Induction with lacUV5 promoter

benedik at benedik at
Thu Oct 26 15:21:28 EST 1995

In article <46ljm7$ed5 at>
patel_p at (taylor) writes:

> Hi:
>         What fold induction is expected with a fully induced lacUV5 promoter.
> I understand, that induction may vary with certain growth conditions and the
> strain of E. coli used.  However, I was wondering the approximate number
> (2X, 4X, 8X or 50X) between the level of expression without an IPTG being
> present vs. >200 mM IPTG present in the medium.
> Thanks in advance
> Prem
> e-mail:     Patel_P at

The lac operon in single copy on the e. coli chromosome has an
induction ratio of about 1000-fold. However you never see that ratio
with plasmids because you can never achieve the same level of
repression. So the answer to your question will depend upon the vector
and host system. But if the plasmid carries the lacI gene on it, you
should get repression ratios of 10-100 fold. If you are relying on the
lacIq allele in the chromosome of many cloning strains, then you will
get a very low induction ratio, because the plasmid is basically on
without inducer since there is not enough repressor in the cell.

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

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