subcloning in XL-1 blue

Willi Jahnen-Dechent ph +49 6131 395793 fax +49 6131 394743 Jahnen at MZDMZA.ZDV.UNI-MAINZ.DE
Wed Jan 25 12:16:51 EST 1995

Dear sub-cloners

We have had trouble to subclone using XL1 blue bugs.  When all reagents
were tested on several plasmids and hosts the problem eventually boiled
down to the XL1 blue cells.  Funny enough, after transformation with
straight bluescript II we got more transformed colonies the more ampicillin
we added to the plates. The only explanation we were offered by a bacterial
geneticist was that probably our bugs went through a lot of generations
already (true) and had mutated to produce so much plasmid, it actually
became toxic.  This fits our observation that the few colonies that we get
produce oodles of plasmid.  Has anyone had similar experience and how can
we keep the XL-1 blue cells the way we bought them (a while ago)?

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