28/4/52
Dear Lederberg, _
Hayes writes me it would be best if the sending of both
_his and our paper to JGM were delayed until June. I have nothing against
g it, on the contrary ; because in such a case 1 might unde:take myself the
trouble of whiting this second paper. This of course unless you have al-
ready started w sting it yourself. Unéfrtunately my English is rather
raw - less raw/HRESY EE would appear from my letters,especially if they
are written in a hurry. I can probably get someone, however,to correct it
in order not to leave this job entirely to you.
One more point about the cultures you sent me ; I have a
_ recollection of a lapsus calami in my last letter. Did 1 write you in a
PS. that your cultures were all right ? They arrived safely,but ali of
them were unfortunately sterile, If you undertake another sending, could
you add 679,which was accidentally discarded, Ma
i I had promised a summary of Hfr work. In Jaad,1949 two
mutants (B,less and arginineless) were prepared from Hfr and crossed to-
‘ gether on BM minimal +BM pnbee recombinant out of 104 cells was the yield
consistently obtained in expts. Hfr activity of both BMB,- and BMAr—
was checked against w 583.Back mutation rates of Bither the two strains
on BM minimal 1076 ana 1077 resp. Also ;: BMB|-Hfr x W 583 on minimal BM,
flo colonies which were M- were isolated. Of these,8 were crossed to W
583 on minimal and none gave a recomb.rate higher than 58-161 control.
q Later (Nov.1949) nicotinicless and pag ra™aineless mutants were isolated
% from W 1073 (Hfrlac-Mal-). Yields o fr x Hfr crosses with these and
{ the above two strains were againg 1074 only for BMB)|- x BMAr=- on minimal
y+ BM,and 10-5 for BMB,- x W 1073 H-. All other crosses less than 1079, Mu-
i, tation rates lower than this figure .
3> W073 kms H-’crossed to BMB,- Hfr on minimal BM. 5 Lac-Mal+ recombinan-.
% ts and 5 Lac+Mal- recombinants crossed on minimal to W 677; all had a
‘) Fecomb. rate. well below that of an Hfr control. fo oO

oul
{ All of the Hfr derivatives mow in my hand have lost their Hfr power,

4)

except the original strain which has been reselected regiularly. I have
therefore to make new mutants’ to test check this unexpected Hfr x Hfr

cross resulting in Nfr progeny. At the time these experiments were made
instability of Hfr had only been suspected and all the relwvant controls
had not: been set up. However I trust they can be reproduced,or at least

.9 hope SO.”

f§ Another point of some interest was that the segregation ratios were unal-
tered,whether the more abundant parent was Hfr or Nfr. I am trying to
reproduce these results now,to see whether this "interference" between

<"gametes"can be confirmed in a variet of combinantions, or whether more
than one gamete can fertilise the safie opposite "gamete",

2 The Laec+S¥ selection undoubtedly gives extraordinary results in the Hfr x
Nfr cross. I wonder wf you have made any progress with it. I had to stop

YY work almost completely ig the past month and am at the moment proceeding

at reduced rate. I have confirmed,however, that attenuated Hfr does trans-
duce F+ . UV-irradiated Hfr does not transduce F+. Would you be kind enou