June 25, 1954

Dr. Ed Adelberg
Bacteriology Department
University of California
Betkeley 4, California

Dear Ed:

I'd promised to keep in touch with you as regards our experiments on diploids
from interrupted matings.

Itm sorry to say that Our results with the Het stocks on hand have been rather
disappointing, the yield in various cross es running about 1 diploid per 100 or so
prototroph recombinants, This is altogether too tedious, so we are setting up some
balanced marker systems which will pre-select heterozygotes. This has worked out
rather well in the past, but we have to make up whole new constellations of stocks
to fit the present problem, and in order to focus on Hfrg (as the most thoroughiy
studied Hfr.) The preliminary results are encouraging if the sense that I think
we can still attack the problem by thds route, but we Mve no results as yet.

We have had a great deal of trouble with the instability of all our Hfry stocks,
as they have an irrepressible tendency to revert to F*, Have you run into this
problem? We have some rather recent transfers from Hayes’ own shipment, so I don't
imagine we have especially troublesome cultures.

You indicated that you wanted to try your own hand independently at the diploid
problem, with your own marker combinations. I am enclosing what vee probably our
best Het Fo at the present time: We2723, whien is Het F> Lec,~ TLE,-"~. We
tried heterozygosis for Lac as a means of diploid selection, for various reasons
this proved an inefficient system with Hfr,. However, at least for qualitative
examination of diploids, you will get some by crossing Hfry 1 x W-2723 on EMS Lec By
medium, and examining a sufficient sample of Lac* prototrophs,

I still am discouraged by what we will be able to learn that would answer the
question why (e.g. in our 195], PNAS paper) the Mal marker was hemizygous even when
of paternal origin, but there is nothing better to do than see what happens with
Hfry and timed interruption, The distinction between hemi- and homo-zyzpsity is a
crucial question, ard unfortunately rather tedious.

Luea Cavaili will be leaving next week; we've had a splendid time on these experi-
ments and will of course be continuing them. We have not succeeded in completing any
x crucial tests of the mechanism of interruption. He and Esther have been very busy
time-mapping the innumerable mutants in the various Gal cistrons, which are not more
than secoms apart from one another. We are looking forwarding to seeing Francois
at Royaumont next month-- will you be travelling this sanmer, or are you sensibly
staying home?

Best rerards

Jostua Lederberg