lacU169

Mikhail Alexeyev malexeye at JAGUAR1.USOUTHAL.EDU
Fri Oct 17 14:23:40 EST 1997 

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> In article <3Q$lVHAWKgR0Ewme at demon.co.uk>, "Dr. Duncan Clark"
>  writes
>
> >It doesn't produce lacI ie pUC18 plated on Xgal (with no IPTG) gives
> >blue clonies.
>
> I've had a look since posting and deltaU169, deltaX111 and deltaX74 are
> deletions of the entire lac operon. DeltaX111 also deletes proAB as
> well.
>
> Info on page 247 of NEB catalogue.
>
Two notes of caution, though:
1. It seems to be well-documented that multicopy plasmids (like pUC) do
not need IPTG for induction in strains that carry wild-type lacI in a
single copy: multiple copies of lac operator (on the plasmid) do titrate
out repressor.  lacIq has a  promoter  up-mutation in a promoter that
leads to appr 10-fold overexpression of the repressor.
2. lacI does not seem to be a part of lac operon, therefore, deletion of
lac operon only SUGGESTS that lacI is non-functional.

M.A.

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<HTML>
&nbsp;
<BLOCKQUOTE TYPE=CITE>
<PRE>In article &lt;3Q$lVHAWKgR0Ewme at demon.co.uk>, "Dr. Duncan Clark"
&nbsp;writes</PRE>
</BLOCKQUOTE>

<BLOCKQUOTE TYPE=CITE>
<PRE></PRE>
</BLOCKQUOTE>

<BLOCKQUOTE TYPE=CITE>
<PRE>
>It doesn't produce lacI ie pUC18 plated on Xgal (with no IPTG) gives
>blue clonies.&nbsp;

I've had a look since posting and deltaU169, deltaX111 and deltaX74 are
deletions of the entire lac operon. DeltaX111 also deletes proAB as
well.

Info on page 247 of NEB catalogue.</PRE>
</BLOCKQUOTE>


<P>Two notes of caution, though:
<BR>1. It seems to be well-documented that multicopy plasmids (like pUC)
do not need IPTG for induction in strains that carry wild-type lacI in
a single copy: multiple copies of lac operator (on the plasmid) do titrate
out repressor.&nbsp; lacIq has a&nbsp; promoter&nbsp; up-mutation in a
promoter that leads to appr 10-fold overexpression of the repressor.
<BR>2. lacI does not seem to be a part of lac operon, therefore, deletion
of lac operon only SUGGESTS that lacI is non-functional.

<P>M.A.</HTML>

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