Composition of M9 media.

Michael Szardenings msz at bio.embnet.se
Mon Oct 16 06:08:11 EST 1995


In article <1995Oct11.124228.63440 at cc.usu.edu>, sl3wx at cc.usu.edu wrote:

> Hi netters,
> I would be grateful for some information regarding minimal medium. 
> I am trying to express a protease via E.coli XL-1 . The bug grows very 
> slowly in LB media (the expression vector is pIN-III-ompA 2 ) and I can 
> see a band on a Cooomassie Blue gel at a position corresponding to the 
> pure enzyme. 

Sorry, but forget about XL-1 in this case. pIN-III vectors have a very
strong lpp-promoter (normally constitutive) regulated by a weak lacI
binding site. The extra repressor gene provided on the vector does not
help enough, if you have a potentially toxic gene. You need a very
'healthy' strain in this case. I would try strains like JM83, JM101 or
dM15. They are producing already high amounts of lacI gene product. 
For good expression: NO M9-medium
   -freshly transformed cells
   -try growth in presence of glucose (ca. 1%) or glycerol (0.5%)
   -very good aeration 

Choose another vector, if this does not help

good luck 

               Michael

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