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Constitutive Fusion Protein Expression in BL21(DE3) Cells

C.L.L. ChunLin_Lu at cellbio.duke.edu
Wed Mar 6 23:10:59 EST 1996

In article <biotech-0403961716060001 at cyto.cytosignal.com>, biotech at ni.net
(David J Benz) wrote:
 What we've noticed is that lately our proteins are
> beginning to show up in uninduced bacteria. The tac promoter is supposed
> to drive transcription, and shouldn't be active in the absence of IPTG.
> Why are our proteins expressing in uninduced bacteria?
It is true in most cases, not in all.  I expressed six different kinds of
proteins in BL21 system and found that some of them did make protein
without IPTG induction, and got same amount of it. After sveral passages,
it disappeared. One protein which is very toxic to bacteria, failed to
make in plain BL21, but did in BL21/plys S, no activity. I dont know what
cause your expression constitutively, it was once disscussed in this group
on this matte, I can not remmember what they posted.

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