fresh transformations for protein expression??

Jennifer Lyon JLyon at
Wed Jan 31 19:05:12 EST 1996

M. Alexeyev wrote:

>Besides, if I am not mistaken, Novagen guarantees BL21 (DE3) for only six
>month at -70. That would also suggest to me some instability of T7pol+
>phenotype in this strain (other strains could be stored for much longer
>periods at this temp.).

Actually, the cell strain BL21(DE3) (without an expression plasmid in it) 
should be stable as long as any other glycerol stock of e.coli. The 6 months 
guarantee is just standard policy for all of our products with the exception 
of the competent cells which are guaranteed for 3 months. Some of the 
products, like plasmid DNA's and glycerol stocks are certainly good for much 
more extended periods of time, and I know we have working stocks of the 
bacteria in our lab that are older than 6 months and are still used without 
trouble. The problems that show up in these strains occur when the expression 
plasmid is stored down in the expression strain. It does indeed appear to be 
something that happens to the bacteria, since the plasmid can be recovered 
and retransformed to recover full expression. I'm not sure why it happens, 
but I'd suggest keeping a stock of the plasmid DNA separate from the 
expression strain.

-----------------------------------------------------------------------------JennyAnn at                   JLyon at
"Sometimes the need to mess with their heads outweighs the
millstone of humiliation."  Fox Mulder  "The X-Files"

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