Expression of toxic protein

Thomas urbig at
Tue Jan 27 02:58:07 EST 1998

In article <6a6iak$6pp$1 at>, wsyang at
(Wan Seok Yang) wrote:

>  my recombinant protein is large(>100kDa) and toxic.
>  When I transformed the vector only ~20 colony appeared that's 
>  about 1/500 efficiency compared to parental vector.
>  So I introduced LacI vector to host(BL21(DE3)) and much more 
>  colonies appeared. But after IPTG induction the cell die.
>  Most manual emphasize down regulation of basal level however
>  they don't comment cell death after IPTG induction.
>  Can I get my recombinant protein?
>  (when survived ~20 colonies were tested for induction some of them
>  showed induction band but I can't believe they are active...)

Try the higher stringency host Bl21(DE3)pLysS or BL21(DE3)pLysE (for
highest stringency), available from Novagen or the helper phage carrying
the DE3 (available from Invitrogen- it's not in the catalogue!).


Thomas Urbig
email: urbig at

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