BL21(DE3) and trc promoter

ChenHA hzhen at
Tue Feb 8 17:49:44 EST 2000

Petri Kursula wrote:

> Confused by all these E.coli genotypes and strains, I would like to know
> if anyone has used BL21(DE3) cells to produce recombinant proteins from a
> vector with the trc promoter, such as pTrc99a. If yes, is this expression
> tightly regulatable by IPTG, or do you get leaky expression?

This is likely to be leaky.  I haven't used pTrc99a for a long time, but I
think it has a lacIQ which should help with the regulation.   In general, as
long as the expression is reasonably well-controlled, it should be OK if your
protein is not toxic to the cell.  You only need to worry about how tight the
regulation is if your protein is toxic, in which case pTrc 99a is a bad
choice and you will have to consider using other vectors.

BTW, the (DE3) bit of your BL21(DE3) is unncessary for pTrc99a.  If you are
confused by the strains, all you need to know is that there are cloning
strains and there are expression strains.  Bl21 is an expression strains.

> -----------------------------------------------------------------------
> Petri Kursula           "I am somehow less interested in the weight and
> University of Oulu    convolutions of Einstein's brain than in the near
> Petri.Kursula at  certainty that people of equal talent have lived
>          and died in cotton fields and sweatshops."
>                        -- Stephen Jay Gould
> -----------------------------------------------------------------------

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