Dr. Duncan Clark duncan at
Mon Oct 20 04:05:05 EST 1997

In article <3447BB08.C339F181 at>, Mikhail Alexeyev
<malexeye at JAGUAR1.USOUTHAL.EDU> writes
>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.

Agreed but given that deltaX111 also deletes proAB, logically it must
have a lacI deletion because lacI is between proAB (6mins) and lacZ
(8mins). The best test would probably be PCR using primers against lacI
(nice simple useful paper!). Also on page 53 of Jeffrey Miller's
Experiments in Molecular Genetics (CSH) there is a complete list of
indicator plate reactions for Lac ie i,z and y mutations and mixtures of

The problem with being on the cutting edge is that you occasionally get 
sliced from time to time....

Duncan Clark
DNAmp Ltd.
TEl/FAX 01252376288

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