BL21 Codon-plus

ChenHA hzhen at
Thu Nov 9 19:02:14 EST 2000

Mizar wrote:
> Hi everyone,
> After many efforts, we are not still able to express our recombinant
> human protein in E. coli. so we are thinking to switch to codon-plus
> strain.
> Someone tried the BL21 codon plus (DE3) strain from Stratagene?
> Another question: there are 2 strains with different tRNAs:
> both have the AGA/AGG tRNA but
> RP posses the CCC tRNA
> RIL posses the AUA and CUA tRNAs
> In my gene I have 6 CCC codons and 4 AUA + 3 CUA codons;
> do you think it's better to overcome the 6CCC problem (RP strain)
> or the 4AUA+3CUA problem?
> In other words are more problematic 6 unusals codons of the
> same type or 7 unusal codons of different types?

I would choose RP unless the other rare codons are present in
clusters.  Normally a few rare codons doesn't make much difference to
the expression, but large number of one particular rare codon may
affect expression.  The problem with advice like mine is that
sometimes the effect of the codons may be context dependent, therefore
a rare codon in a particular site may be particularly deleterious for
protein expression.  I have tried RIL cells but it only helps with the
expression of some proteins. 

But what wrong with trying both?  

Note also that codon usage is not the only determinant of protein
expression and your problem may lie somewhere else.  

> Thank you for your attention.
> Bye
> --------------------------------------------------------------------------------------------
> Gianluca Molla Ph.D.
> Dept. of Structural and Functional Biology, University of Insubria
> via J.H. Dunant 3, 21100 Varese (ITALY), mail:
> gianluca.molla at
> Tel. ++39-0332-421414 Fax. ++39-0332-421500

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