UNIVERSITY OF CAMBRIDGE

PROFESSOR R. A. FISHER, Sc.D., F.R.S. DEPARTMENT OF GENETICS WHITTINGEHAME LODGE
MISS M.F.E SPEYER, B.Sc. 44 STOREY’S WAY
Research Assistant and Secretary ‘ CAMBRIDGE

Tal. 55822

Nov. 2th, 1949
Dear Lederberg,

Thank you very much for your letter of the gH i pan
sending you under separate cover 123 and a derivative, 123 Lac3-V, 5?

whéeé¢h when crossed to 58-161 or 58=161 Hfr gives recombination oBboth

4o 123
characters. It is interesting that Nfr and nerVgive different rehom-

ales ol

bination values, though the’ rate of recombination is apparently tke

same. Lac. crossed to W 10%3 gives recombinants which are partly Lac+,
showing that theyxare Lac genes are not al@blic. Of course I gontt
know whether this 4a 3 is allelic to Lac, of the K 12 series your have
established. I am not sending biochemical mutants of 123 because I have /
not yet any reliable ones; I waited to answer you,hoping I might have ‘
had some by now, but unfortunately this work is still behind.

Crosses Hfr x Hfr with new biochemical mutants seem to
give very poor yieds, and Arsxisxezxiz Ar- x B- is the hest-yielding
of all of them ( 10 4,10 ° +; perhaps | shall heve to return on wy sta-
tement about mating types !

-The cross W 81 x W 1059 or W 1073 did of course succeed
when I used neuéréent-breth-er penassay broth instead of nutrient broth;
reasnr@ of the discrepancy will,I hope, become clear when an experiment

now being made will be finished. I have also tried the ating ox a® 5
im seems that with this method as well, Hfr gives better yields than
Nfr ( 58-161 + but the ratio is on.y about 100 times.

I heve done some work with the salts, but so far no

important results have come out. There are,of course,differences, and

formulas favoring the formation of insoggble compounds like Mg-NHp pho-

sphates seem to give poorer yields
9
I had a letter from Maaloe,to whom I am sending the nearest aporo-
ximations to the strains he wants which are in my hands ; they should
%e however be quite satisfactory for his purposes. As I am doing a si-

milar work on Hfr, as he tx/aoine on Nfr, it will be xXexy inter@sting
to compare our results.
It was most interesting to hear from you of the new coli strain
showing recombination. Have you any idea of the denominator of the
fraction of strains showing sexual reproduction, i.e. how many sbrains
have been tested for mating behaviour ?I am doing again something on
that line this year.I hope to have it soon,and mampare see whether it
mates with 123 . Inciadentally,123 is not so very different from Kie.
It was not tested for Viruses T4-T6, because I have lost them ; samples
of viruses .
‘I fedkfrom Milan in October were not reliable,snd I shall write again
to the States or to Latarjet to have those viruses. With Te 123 wave
irregular results ,but should be defined as sensitive . It has a peculi
ar difference from Ki2m ,in size of colony; colonies of 123 aresmall
on all media I have tried. It must be a polygenic character; however it

wives a not too bad segregation when crossed to Hfr (no segregation wh
when crossed to Nfr ) . For s:igars, I did not find differencesm ,so fap
with K 12. I know nothing about the Origin of 123 ; but I should write
to the NCTC about it.

As to the question of radiation-i::duced lethals, I am most intere
sted to hear thet you will cazsry on that research ; I think it wdauld be
weew interesting to do it with X rays as well as with UV, they will pro-
bably give cameposiana’ results. I shall be grateful if you will tet me

know about some of your results,and of course I think it is better if
in
this research will be carried on ky yourseit#y rather than in my labora-
tory.
Did you try anything for recombination of lethals ? A start with

Hfr was fully negative, but it may be that the new techhiques of croggig

in complete media, which you have developedy: may give a different answe

wer.

Concerning cytology : nothing done so far nn my side. I hope you
will be more successful with diploids.

Yours sincerely