genomic DNA contamination using Wizard plasmid kit

Neil Saunders neil.saunders at
Tue Jun 5 02:10:11 EST 2001

Dear group,

We are currently using Promega Wizard plasmid miniprep kits to try and
detect plasmids in archaea.  The preps are a bit inconsistent, but we seem
to be seeing a discrete band of around 18-20 kbp.  The problem comes during
restriction digests-under normal conditions we see a smear reminiscent of
chromosomal digest, less enzyme/time seems not to cut at all.

Because of the size and appearance of the band, I wondered if it could be
chromosomal DNA contamination.  Has anyone ever seen this with a Wizard
plasmid prep?  I'd have thought that the precipitation step should remove
all chromosomal, but we are using a lot of cells (low final OD), so I
wondered if overloading could be a problem.  Although the band doesn't look
chromosomal (below the lambda 23 kbp and quite discrete), it doesn't look
quite plasmid either, especially when digested.

thanks for any thoughts,

Neil Saunders

School of Microbiology & Immunology,
University of New South Wales,
Sydney 2052,
NSW, Australia

Ph: +61 2 9385 2093
Fx: +61 2 9385 1591

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