Paul N Hengen pnh at fcsparc6.ncifcrf.gov
Wed Dec 8 15:29:42 EST 1993

Caroline A Breitenberger writes:

| ...To summarize, XL1Blue has an F' episome without which you cannot
| do blue/white screening.  Check your cells on tetracycline to make
| sure they retain the F'.

A better control is to transform cells with uncut M13 DNA. If the E.coli has
lost the F factor, you will not get plaques since M13 infects through the F
pilus.  Selection of XL1Blue cells with tetracycline may lead to insertions of
Tn7 in the chromosome because that is the source of antibiotic resistance on
the F plasmid in that strain. I've always wondered about this, so does anyone
know what makes F' more stable in DH5aF' than in the older JM101 or JM109

* Paul N. Hengen, Ph.D.                           /--------------------------/*
* National Cancer Institute                       |Internet: pnh at ncifcrf.gov |*
* 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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