protein expression

ChenHA hachen at bc.ic.ac.uk
Thu Mar 18 08:01:46 EST 1999

On 17 Mar 1999, Wolfgang Schechinger wrote:

> What about adding Glucose to the medium? It should lead to 
> suppression of the lactose operon. For induction, add IPTG. 

Nope.  Most, if not all, of the lac operon used for expression of
protein are lacUV5 mutant, which make it insensitive to catabolite
repression (i.e not affected by glucose).  Otherwise you won't be
able to control the lac operon at all for many media which use glucose
as the sole carbon source (although some think that there is some
residual effect and that adding glucose do have some slight effect in 
controlling protein expression).

Back to expression problem, there are many reasons why you get poor
expression of protein:  N-terminal sequences, codon usage, toxicity
etc.  A useful place to start is Novagen website at


Take a look at the protein expression FAQ, it doesn't list all the
possible causes, but useful nonetheless.

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