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Why is sacB expression lethal in E. coli?

Brad Nicholson brad_nicholson at hlthsci.med.utah.edu
Mon Oct 21 15:09:12 EST 1996

>First reply snipped, my apologies.<
> REWH Lab <rewhlab at cbdn.ca> wrote in article <53udca$jl1 at nntp.ucs.ubc.ca>...
> > Hi,
> >       I can't find any reference to why sacB functions as a 
> > counterselective marker in E. coli in the presence of 5-10% sucrose. 
> Does 
> > anyone know why it works?
Gay, P., D. LeCpq, M. Steinmetz, E. Ferrari, and J.A. Hoch. 1983 Cloning
structural gene sacB, whyich codes for exoenzyme levansucrase of Bacillus
subtilis: expression of the gene in Escherichia coli. J. Bacteriol.

Quick answer;  sacB produces levans (branched chain sugars, supposition
mode on, that pile up in the cytoplasm or periplasmic space, resulting in
lysis on hypotonic media.)  That's why you don't add any salt in your LB
when you are performing your selection.

Good system.

Brad Nicholson                      |"If it worked the first time, 
Department of Pathology             | it wouldn't be research.'
University of Utah                  | ...Brad Nicholson
Salt Lake City, UT 84132            | My opinions are solely my own.
brad_nicholson at hlthsci.med.utah.edu |
or: (801)-581-4365                  | iligitimi non corborundrum

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