UNIVERSITY OF CAMBRIDGE

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

Tel. 55822

22/7/49

Dear Lederherg,
I am sorry for my delay in answering, but T sent you the

strains about ten days ago and I know they take longer tine than letters.

I sent vou 58-161 Hfr ,whiech is also labelled BeL-Ny® (though tT have never

tested whether it still is biotinless or nog 7 glucose contains karfx encugh
of 58-161

biotin to rive half prowth/in -rsence of methionine send I never bothered to

vg
eliminate) follows
ollowing

Before sending you Hfr I have retested it,and I got the/fesults:

plating on surface with vitamin By io, of vrototrovhs :

No. of cells of Bel-Ny”®

29100 210! 2 10° 210? 2104 2103 210°
No.of cells
of W §83 8 3
2.5 10, 3 7 10; 510 128
2.5 10¢ 3 ? 10 ~10
2.5 10 >10 7103 101
2.5 107 ; 93+ 209 253 215
2.510" $10 670 missing 256
2.5102 ~ 107 glyph ent,
2.5.10 267
same without vitarin By
2.5 103 7 103 >10? 387
2.5 10; 510 422
2.5 10 16 78 112
2.5 10° 6 2
2.5 104 6

T use Ditco agar which geve me so far good results without any trestment, but
it fro jpeey likely that using a more purified medium might decrease vields.

As to other peculiarities of the strein,vou will find them
in the enclosed paper which T save ait the 100th meeting of the Geneticel

Society,in Cambridge, the 3¢th of June. Later I tried Hfr with W 826 ana
W 836,with wrich it mates at a higher rate bhan 58-161,bdut the difference is
less striking than with W 583.

I am very 2nxious to know whether it will work properly in your
conditions. I «em sending you also B-M-Ny"B, =» which is a biochemical mutant
I obtained from it ; it needs elso vitamin By for erowtth, but such 2 gene is
not allelic to By- of W 683 3 vlating this strein with VW 583 one gets recon-
binants in absence of vitenin By at rete 107° - i07!, and it is in these con-
ditions that I obtained the possibile diploid I mentioned in the paver: it
gave regularly mottled colonies on lactose and arebinose,urfortunately I
lost it on the third subculture. It may prove useful in your studies on
heterozygotes.

As to the reasons why Hfr behsves ~-s it does, IT have not been able te
reach a definite conclusion, but I shell try fo on with this problem. I agree
that differences in chemiotrovie behaviour may be important . But the main
use for me of this strain will be to try to make matings controlled under
the microscope, and follow meiosis by isolation of early products of division.
It mey hean a full waste of time, but I think it is worth trying.

As a@ consequence of the work with Hfr,I started with a Frennhman who

has been working with me some time,2 preliminary exploration of rossible

'
mating types. The research was nerstive under tha¥point of view,but was

successful in f-iving another coli strain showing recombination. The situa-
tion is still very obscure, and the fact thet most of the charscters are of

one varental tvpe only made me long doubt whether there wes any recombinntion

at 11. Eventually I got some re-co-bination, mak caalcsinare ie -ecaiaae HE

 

emnenty elh\y I am enclosing 2 cooy of a letter I just sent to N=ture.

Linearity : T am a priori convinced of linearity,beccuse I can hardly
think of a noh-linear system showing the regularities of recombination which
your bacteria do show , But no doubt there sre difficulties te reconcile

this with the data, I am often fancvinge whether in the building of strain
UNIVERSITY OF CAMBRIDGE
PROFESSOR R. A. FISHER, Sc.D., F.R.S. DEPARTMENT OF GENETICS WHITTINGEHAME LODGE

MISS M.F.1.SPEVER, B.Sc. 44 STOREY’S WAY
Research Assistant and Secretary CAMBRIDGE

Tel. 55822
W 583,and vossibly in its three first sters, thus affecting ell

derivatives, a chronosome mutation may have slinned in. I am also wondering
whether it might not be worth while,though a very long job, to mee egain
a ‘YT 583 starting frou the original F 12 and see whether,after check of all
allelisms, it fives the seae man. IT sheuld not be surprised if the new straivz
aove By end possibly xylose and something else an snother chromosome. I am
very interested to hear that your data on Lac and Wal in heterozygotes support
the idea of a chromosome aberration.

T am leaving now for e holiday in my wountry . T should be crateful

if you could send me, in sentember, the Lfr strains you mention in your letters;

I should also be interested in heving the original K 12,98,if I shall ever
have the courage of starting the programme of rebuilding W 5°3,it is better
to start with the originel strain rather than whih a back mtent.

If you write me to Cambridge your letters will reach me only with

a delev of fev days. Hoping your summer work will be succeséfuly

Yours sincerely