E. coli genotypes

Chris Boyd chrisb at hgu.mrc.ac.uk
Fri Mar 21 07:41:00 EST 1997

Nancy Linford (nantzee at u.washington.edu) wrote:
: Hi. Thank you all for your helpful replies in the past. I have a couple of
: questions that have been bobbing around the lab

: 1) WHat is the difference between a RecA13 (HB101 cells) mutation and a
: RecA1 (XL-i blue, etc...)? Both are listed as mutations which reduce
: recombination. However, by experience, our plasmid recombines like mad in
: RecA1 cells but is reasonably stable in RecA13 cells. Does anyone know the
: difference?

They are different alleles of the recA gene.  Your evidence suggests
that recA13 is less leaky (in terms of residual recombination) than
recA1, which I suspect is a Previously Known Fact: there was a paper
some time ago tabulating the various recA alleles, their sequences and
recombination properties, but I've mislaid it.  If you are really
concerned about residual recA function, go for strains that have recA

: 2) Why do cells containing the F'episome need to be grown on minimal media
: to maintain infectability? It would seem more likely that in a "stressful"
: medium such as minimal they would be more likely to save their energy
: and not maintain pilli. 

Because the F' in question contains Pro+ genes, while the host cell
genome is Pro-.  Therefore, cells that have lost the F' cannot grow on
minimal medium, but are perfectly healthy on medium containing proline
(such as L agar).

Chris Boyd                       | from, | MRC Human Genetics Unit
chrisb at hgu.mrc.ac.uk             |  not  |  Western General Hospital
http://www.hgu.mrc.ac.uk/~chrisb |   for |   Edinburgh EH4 2XU, SCOTLAND

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