Lonc ISLAND BIOLOGICAL ASSOCIATION
COLD SPRING HARBOR, NEW YORK

THE BIOLOGICAL LABORATORY 5 May. 1955

Dr. Joshua Lederberg
Genetics Department
College of Agriculture
' University of Wisconsin
Madison, Wisconsin

Dear Josh,

Thanks very much for sending the Hfr cultures so aiickly. I'm finally
returning the acknowledgment of receipt. I tried to cross 42323 (Hayes' Hfr)
with W1177 upon receipt and got nothing. I haven't looked at it since, so I have
no idea what the difficulty is. The fai’t is probably mine somewhere end J'll try to
check fore fully later, but thought the incident worth mentioning. —

The tracer experiments have gone quite well and are consistent with a
unilaterally biassed flow of DNA from Hfr to F~. ‘We would like now to make some
estimate of the fraction of parental DNA involved. This depends, among other things,
on a reliable estimate of the number of zygotes formed under our conditions. “e
have dta on this, but there are some peculiar aspects of the situation that we wogld
like to discuss with you, particularly with reference to what you find in dissected
clones. Since vou will be in NYC on May 19, I believe, we wondered if you could
come out to Cold Spring Harbor for at least half a day swrkwe at this time.

Norton has said that he would be glad to drive you out here and back to the city.
Linda and I will be glad to feed you and Esther, and arrangements can be made if
you are able to stay ov-rnicht. Hershey is quite interested in the problem and
would like to sit in on discussions.

Tf vou cannot make the trip, Alan and I could come into NYC if vou will have
any time to discuss things there. If neither arvanfement works out we'll send you
a summary of our difficulties by mail as soon as possible. .

In anticipation, here is a brief presentation of the most troublesome situation.
Hfr V5 v¥ lac# M- is crossed with F- v3 Vi lac- TLB|- at a low Hfr:F- mltiplicity,
0.3 or less. The Hfr +s hot. The F- and gotes are lysed with T2 and radioactivity
in T2 measured and compared with total uff radioactivity, An aliouot of the sane
cross is treated with T4, lysing Hfr but sparing F- and zygotes, and plated on
=EMB-lac. The number of colonies sectoring for lac is a minimal estimate of zvgotes
formed. This xuxahemkx2ifxet indicates that at least 25% of the Hfr contribute to
zygotes. This does not do justice to the experiment, sime several obvious difficulties
are not mentioned; but it is sufficient to show that one difficulty is in knowing
how many zygotes are not detected. On an (--E~--lac----L---T) map, Lf recombinants
should be more common than lac/, but they do not seem to be. Most recombination
of other markers is concentrated in lac sectored colonies, and only about 40% of
sectored colonies contain Lf. If this. flees not involve an artefact, it should be
paralleled in your single cell studies by a high incorporation of lacf as opposed to
L4. Incidentally, the sectors are not papillae, and do not appear in F- x F-.

I hope we will see you in two weeks.

Sincerely,

Dane

Dave Skaar —