lac- selection in E.coli

Michael Benedik benedik at uh.edu
Mon Dec 1 09:51:26 EST 1997

In article <cdsouza-2611971812320001 at adams-centris660av.tamu.edu>
cdsouza at bio.tamu.edu (Biology) writes:

> Does anybody know of a nifty way to select for lac- E.coli on LB media.  I
> am aware of positive selection vectors but is there a substrate that's
> converted to a toxic product? Thanks.  Cletus
> cdsouza at bio.tamu.edu

Two classic selections for lac- are TONPG which is a toxic compound
that is accumulated by lac permease. This selection gives lacY- mutants
some of which are also deletions of Z or polar mutations in Z.

selection on lactose using a galE mutant strain. lacZ converts Lac to
glu and gal, and growth on gal with a galE mutant is toxic.

I would suggest looking at either volume of Miller (CSH 1972 Expts in
Molecular Genetics, or CSH 1992, A short course in bacterial genetics.)
The older volume discusses more compounds, the newer volume describes
the above 2 in a bit more detail.

P.S. Give Ry Young a call for more info.

Michael Benedik
Department of Biochemical Sciences
University of Houston
benedik at uh.edu

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