cloning problem

Bryan J. Maloney dogface at
Wed Sep 25 20:58:53 EST 2002

Britta Satzke <bsatzke at> wrote in news:3D91CA72.B2287E2 at

> Hi, there
> all lab members have had some cloning problems for two weeks now:
> 1. When subcloning in DH5a we get 2 types of colonies: big and small
> ones.
> 2. After Mini-DNA-prep we always get two bands (size 3kb + 1.8kb)- no
> matter which vector and insert we use, nor which restriction enzymes we
> use.
> We get low transformation efficiencies with Midi-DNA, transformation of
> ligation doesn´t work anymore.

You have a bacterial contaminant that has overwhelmed your culture.  Go 
back to clean DH5a stock.

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