Contaminating plasmid

Dave Harry deh at
Sat Jan 15 13:38:14 EST 1994

>I have absolutely no idea what it is, but I've had the exact same thing
>happen, TWICE.  I have only seen it with pBluescript, a plasmid of the
Ditto my experience.

>size you describe which doesn't cut with the appropriate enzymes.  I even
Again, ditto.
>3)Reappearance of this unusual plasmid has occurred only when I use
>  Xl1-blue cells. I had reordered new plasmid from the company, it was fine
Again, ditto.

>  new stock and grew in HB101s instead, quite some time later, there is
>  still no problem.

Nearly ditto.  I used DH5-alpha.

I shared Sheryl's frustration in her experience.  This "mystery" band
caused endless grief a couple of years ago.  It kept cropping it's ugly
head and caused mass confusion.  I also made some hand-waving arguments
about leaky f1 origins (as in earlier posts) and further speculated that
it might have something to do with XL1-Blue's tet-containing episome.  In
desparation, I called Stratagene for advice, only to learn they'd never
seen this (so therefore we must be some foolish incompetents?!) and could
offer no insights.

In short, I never did learn what it was.  *BUT*, the problem did indeed
disappear after transforming my Bluescript vectors into different a
different host (DH5-alpha).  I now use XL1-Blue only when absolutely
necessary to carry out certain procedures, and then get my plasmids the
H--- out of there as fast as possible and into another host.

Until I saw this discussion, I thought we were the only ones who'd
encountered this problem.  Thanks to all for sharing!!

David Harry                       Institute of Forest Genetics
deh at             USDA Forest Service, Pacific SW Station
Phone:  510/559-6439              PO Box 245
FAX:    510/559-6499              Berkeley, CA 94701


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