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Plasmid instability in E. coli

Weisong Zhou wzhou0 at pop.uky.edu
Thu Nov 5 09:40:02 EST 1998

When I was cloning the envelope and gag-pol genes of a lentivirus
(equine infectious anemia virus) into high copy number vectors, I
usually got recombinant plasmids with correct insert at the first
screening of colonies. However, the plasmids disappeared in the
following several passages ( liquid culture aliquot were used as seeds
for consecutive passaging in LB medium with 100 micrograms/ml of
ampicillin ). In some cases, the disappeared plasmids could come back
again. This was true regardless what kind of high copy number vector or
E. coli strains were used. I tried two vectors ( pcDNA3.1(+) from
InVitrogene and pCI from Promega) and several bacterial strains
including HB101, NovaBlue, and SURE cells. The results were just the

Any suggestions about what's going on and how to get rid of this kind of
instability will be appreciated. Thanks a lot. 

Weisong Zhou (wzhou0 at pop.uky.edu)

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