August 26, 1949.

Dr. Me. RR. delle, . mS
Oak Ridge National Laboratory,
- BLology Division, . "
p.0. Box P,

Oak Ridgs, Tenn,

.,. Dear Max:

_ Most of your old H-148 cultures turned out to be as they should have
been, Xyly. Judgin§ from the only other stocks that I have sent you, the
Xyl- Mtly. type you later got out mist have come from H~168; nothing else
was itly. Howaver, we were unable to reproduce the change from Xyly to Xyl-
in some rather extensive tests.
, I don*t think that there iz mich more that can be done with Hl48. The
Xyly to Jyl- shmge presumably came from a refusion of segregahts, but there
is no way to prove this. The extranely biassed segregations in Hel68 make
imppebable the deshderatum of isolating co-segregants. H-206 should be rather
more suitable for this purpose, and I haven't turned up anything better.

Next month we are going to stumt on the problem of controlling the nuclear

‘gondition of BE, aoli, but I am not very optimistic. We also will try to
get under way a-general study of the cytology of the diploids, and this
may unearth some new ideas. The nugber of nuclei per cell seeas to be
variable throughout the growth oycle, but I have been told that the small
cella of the decline phase may be uninucleate. However, when growth resumes,
cell division already lags behind nuclear division. But it might be worthwhile
using such old cella as starting material for a series of isolations if they
are technically amenable.
Meanwhile, L, Cavalli (4n Fisher's lab at Cambridge) as come out with
an interesting development: a derivative of 58-161 (B-M~ from K-12) which
recombines [i.e. fuses] at an extraordinarily high rate. He is proceeding
with a cytological study to try to define the fusion process, but meanwhike,
I have been trying to get some data on the segregation genetics, by using
his High Frequency of Recombination (Hfr) stock to do crosses on complete
medium, tagging segregating zygotes by their sectored appearance on EMB.
The zygotes kere are not persistent at all, but are formed at a very high
rate, constituting under optimal conditions, as muck as 1/2 % or so of
the total population. If conditions can be found to increase this tenfold or so,
it may become feasible to look for the sygotic cells microscopically, and
transplant them directly, which would be ideal for genetic amalysis. But I
suspect that this is precksely what Cavalli intends to do. What I have
gotten so far on the genetic analysis jibes very well with conclusions
on the heterozygote: All types are not recovered, usually only two, rarely
three (2 parentals and one recombinant) fieasoglemmkx types from a single
segregating colony [i.e. zygote]. There seems to be the same elimination mechanism
which disposes of the Mal+ contribution, that we have seen in the Het diploids
- which are Yal-/... instead of Mal~/Mal+/ In some ways the Hfr stocks will be
* more suitable far pursuing that analysis.

Vety encouragingly, Cavalli-has also found another coli strain (var. acidi-
lactici 123 from the Br, Nat. Type Culture Coll) whieh recombines with K-12. They
do not sgem to be very much alike in any other respects.

Have a good time fishing, _

| Sincerely,
Pos Se

Joshua Lederberg