BL21(DE3) and trc promoter

ChenHA hzhen at
Wed Feb 9 11:38:34 EST 2000

"Michael R. Thompson" wrote:

> Couple of pertinent papers are:
> 'Construction and characterization of a set of E. coli strains deficient in
> all known loci affecting the proteolytic stability of secreted recombinant
> proteins.' Meerman & Georgiou (1994). Bio/Technology 12: 1107. (May be the
> one Duncan referred to), and
> 'Minimizing proteolysis in Escherichia coli: genetic solutions. Gottesman
> (1990). Meth. Enzymol. 185: 119.
> I have succcessfully used some of Dr. Gottesman's strains (which she makes
> available on request), especially SG12036 and SG21173.

I think it should be noted that you cannot knock out all the proteases in e.
coli.   The cell simply cannot survive without many its proteases.  And many of
those that are protease deficient (e.g. Lon- cells)  grow poorly, produce
filamentations and can be horribly smelly.  BL21 is deficient in OmpT but this
doesn't seem to have any adverse effect.

Back to the original questioner - the DE3 bit is unnecessary but it doesn't
affect the protein expression.  It is however necessary if you are using
T7-base promoter.  You can in principle use most E. coli strains for protein
expression, but it is my experience that the dedicated expression strains like
BL21 work best.

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