DH5a w/o plasmid growing on Amp?

David L. Haviland, Ph.D. haviland at KIDS.WUSTL.EDU
Wed Feb 28 01:03:46 EST 1996


On Fri, 23 Feb 1996, Karen Peck-Miller wrote:

> I have a one year old frozen glycerol stock of DH5a which is showing 
> some growth on Lb-Amp plates.  I've ruled out any problem with the 
> plates themselves, and the cultures from this stock have previously 
> behaved as expected (that is, unable to grow on ampicillin).
> 
> I was so surprised by this that I thought I'd ask if anyone else has 
> seen this happen.

Karen:  

I have a totally outlandish thought.  Have you thought of simply growing 
up whatever quantity you wish and doing (conducting) a plasmid prep just 
to see if anything comes out of the bugs?  Then if you see anything, you 
could digest it with something common to polylinkers, such as BamHI or 
EcoRI and see if you can observe any sort of band.  

We had the mis-fortune of "been there/done that"...  our lab had a stock 
of SURE cells that apparently transformed with everything until an 
industrious tech did the ever-needed - bugs with no vector or ligation 
mix alone on a selection plate.  When that was done, BINGO!  We had 
colonies.  A quick and dirty Wizzard revealed some form of plasmid that 
upon digestion revealed a band about 3Kb.  It was likely to be a 
bluscript bug stock rather than a stock for transformation.

Hope this helps,
David

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