the storage of the recombinant plasmid

[Zeng Yitao]

I have constructed a recombinant expression plasmid and kept it in
E.coli Bl21 at -70 degree. Now it seems  not to  be able to express
again, that is, there are some changes for this recombinant plasmid
although stored at -70 degree. Does anyone know how to recover its
expression?

xin Gao
Shanghai Institute of Medical Genitics,
Beijing Xi Lu 1400/24, 
Shanghai 200042,
P.R.China