Paul N Hengen pnh at
Fri Jan 31 13:07:42 EST 1997

Ed Stephenson (estephen at wrote:

> Something similar happened to me once. I had contaminated one of my solutions 
> with a plasmid, which, because it was uncut, transformed much better than the 
> cut-and-ligated DNA that I was using to make the library. I'll bet if you 
> restriction map this clone you'll find that it matches up with a plasmid that 
> you or somebody in your lab is using.

Yeah, don't spend much time sequencing it if it turns out to be the
same size and has the same restriction pattern as pBR322 ;-)

The following is an except from:

author = "P. N. Hengen",
title = "Methods and reagents - Floaties in the gene pool",
journal = "Trends in Biochemical Sciences",
volume = "20",
number = "12",
pages = "522-523",
month = "dec",
year = "1995"}

Initiated graduate students have heard the story about one PhD student who
thought he had discovered a unique antibiotic-resistant plasmid within a
Gram-negative bacterium that was not E. coli.  This student went to tremendous
efforts to sequence much of it, only to find that by running a BLAST comparison
search, the sequence matched that of pBR322. It was only later that the newly
acquired penicillin resistance factor was thought to have arisen from
contaminating plasmid DNA left behind by previous students.

* Paul N. Hengen, Ph.D.                           /--------------------------/*
* National Cancer Institute                       |Internet: pnh at |*
* Laboratory of Mathematical Biology              |   Phone: (301) 846-5581  |*
* Frederick Cancer Research and Development Center|     FAX: (301) 846-5598  |*
* Frederick, Maryland 21702-1201 USA              /--------------------------/*
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