Department of Genetics
University of Wisconsin December 7, 1951
Madisoh 6, Wisconsin

Dr. William Hayes

Department of Bacteriology
Postgraduate Medical School of London
Ducane Road

London W 12. England.

Dear Dr. Hayes:

Thank you for your note of December 3. I am especially pleased to hote
your interest in recombination problems.

I think I can confirm your observations with respect to the action of
streptomycin on sexual fertility. Not long aga, we did some crosses of 58-161
x W-1177 (= W-677 S™) in which the 58-161 parent was exposed to streptomycin,
so as to substantially reduce, but not entirely remove its viability. Yields
of prototrophs were not greatly affected, and, indeed, considerable yields
have been obtained in crosses conducted on minimal + streptomycin agar. We did
not, however, have occasion to conduct the reverse cross, and perhaps for that
reason have not drawn any definite conclusions from the experiment. I would
still suggest that the effect (or lack of it ) of sm could be expressed in simpler
terms: that the treated cells are incapable of sustained proliferation in clonal
reproduction, but can still congress with other cells with respect to sexual
function. The greater sensitivity of W-677 is just that. One reason that I have
not sustained the suggestion of a unilateral exchange is, for example, that K-12
can readily be crossed with B-M-S” or T-L-B_-S* (by plating on minimal-sm agar,
with ofr without prior growth in mixed culture), and the latter can also be crossec
by the usual method. I do not quite see the bearing, one way or the other, of your
result on the possibility that "the agent of ganetic recombination is exuded”
in any way, although this is, of course, as good a working hypothesis as any for
further work.

I regret that I cannot accomodate your request for K-12 auxotrophs that do
not overlap the BM or TLB, series. We have had some rather unsatisfactory cultures
that would not be very usefal, and just now are engaged in regfolating a new
series, with special attention to avoiding the use of mtagenic agents. But this
is part of a program to improve our stocks for crossing some thirty distinct,
interfertile isolates of E. coli from various sources, and it may be some time
before they are ready. I must rather shamefacedly confess that virtually all of
our work with K~l2 has involved descendants of Tatum's first two mutants (58 and
679 of his 1945 paper), and this is not the first incident to make us wish we
had made our mutants extensively, as weil as concentrating them in lines like
W-1177. If I can guess your intentions, however, you might be able to use the
ancestors of W-677, 679-680 and Y-10 (T-L-; T-L-B,- respectively). I have not
looked at these closely for some while, but trust that the cultures we shall
send you will be satisfactory.

The culture "S", described by Weigle and Delbruck may be any one of
several that we sent them; their records have apparently been lost. Mrs.
Lederberg will, however, include %-1485. This is a lambda-sensitive "mutant"
isolated from K-12 after UV. You may be interested that NTCC-123 (Cavalli's
interfert'le culture) is also sensitive to lambda.

I was pleased to note that you had cleared up the strain-component of
the UV effect. My experiments to confirm the UofTexas report gave very spo-
radic, though over-all incontestable, results. The question of a true evalua-
tion of rates of recombination fe very tricky, anc an easily reprcduced exneri-
ment is essential.