danuary 12, 1952

Dr. Marguerite Vogt
Kerckhoff Laboratories

Galifornia Institute of Technology

Padadens 4, Sallfornia.

Bear Dr. Vogts

About fourteen months ago, I sent you a culture of Cavalli's Rfr
etrain, our no. W-1033. I have had no ocsasion to retest this culture
for some tine aince, and could not be sure that it was in good condition
even in October 1950. There 45 an experiment that T should Like to tey
now with Afr, but unfortunately our present culture, only recently lyophilised,
no longer shows any remarkable Hfr activity. If you have had any better
luck than I with it, I would consider it an appreciable favor {f you
eould send back a still active Hfr.

Ne have made no measurable progress to the elucidation of the sschanien
of recombination in Escherichia coli during the past two or three years.
Meanwhile, the only points cof partinent interest have heen the isolation
of other fertile strains of B. coli, and the transductional genetic aschanion
of Salmmehae. Although of interest in other connections, these lines of
work have not cast any light on the K-12 story. In the past few weaks, however,
some evidence has developed for a possible "hormonal" factor in % coli
semality that hag 3028 promise for some progress. A few special cultures
from K-12 nave bsen found to carry 2 "mutation", F-, in contrast to the F+
character of K-12 itself and most of its derivatives. F+ x P+, and Fe x F~ are
both fertile, but F- x F- is completely infertils. At first we thought we
were dealing with a case of "self-ineomeatibillty” sileles, but 1¢ now appeara
that this is true in only a special sense. If an F- is grown together with
a autritionally identical Fe, and this call mixture plated on minimal ager
with another nutritimally compleasntary F-, the markers found among the proto-
trophs show that many of them have come from F~ x F-. If the same cells are
grown separately, and then alixed on miniaal agar, only the F~ x F+ components
will have crossed. The most reasonable interpretation is that P+ 4s responsible
for s substance needed for recombination, and that F+ cells make this substance
to F- sells grown with thea. However, I have aot yet succeeded in separating
an "B+ substance" from F+ cultures, so that cther explanations are possible,
but I think unlikely. What you have probably surmised at this point is that
I should like to test the Hfr stock as possibly producing larger amounte of
the hypothetical P+ fertility factor.
Mrs, Lederberg and I had noticed some time ago that well—aerated
cultures were often poorly or not fertile, and so we have routinely
prepared inocula from standing cultures. This has not been completely
analysed, but it appears likely that part of the aeration effect is
related to the inhibition of the produstion of the F+ factor. Well-aerated
cultures of 58-161(F+)} behave as if they were F-.

We have still to do some quantitative studies on this point, but
I have the impression that F+ x F~ cubsapes may be more fartile generally
than corresponddig F+ x F+. The effect is not spectacular, however.

Hayes, in London, has been doing some interesting work on the ~ o
activation of recombination by UV. He finds that the ,Haas-Wyss-Stone =~ 7 4
effect is entirely due to the 58-161 in crosses with W-1177, and that
the optimal conditions are similar to those for induction of lambda.

In part, I can confktm his findings, but his conclusions that lambda itself
has something to do with recombination are negated by Mrs. Lederberg's
success with crosses of lmbda-sensitive x sensitive.

Some time ago, you mentioned to Mr. Zinder that you were preparing a
note summarizing your work. Has this been publisged?~ I have not seen it.
However, Mr. Zinder mentions that he heard several second-hand reports during
his recent trip on the East Coast, from which he could learn no factual
de&sils, but could concluddethat you have been achieving some success
in your work. Considering the obscurity which has thus far surrounded the
nonOgenetic aspects of E. coli recombination, this will be good news
indeed.

Yours very sincerely,

* Joshua Lederberg
Associate Professor of Genetics