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i POSTEKADUATE’ MEDIGAL SC Z

OF LONDON
Telegrams
POSGRADMED CHISK LONDON DUCANE ROAD

        
 

SETA

‘elephone od .
SHEpherds ‘hah 1260 (4 lines) chy LONDON, W.1!2
Department of Bacteriology. 20th June, 1952.

Dear Lederberg,

I must apologise for not having written to you for such
a long time but I have been very busy during the last six weekse
Nany thanks for the non-lysogenic W-1982. TI have not tried it
yet but I did obtain an P+ non-lysogenic, histidine and cystine-
requiring strain from Lwoff and this responds to UV in exactly
the Same way as 58/¥+ when mated with Wob775 The fertility
enhancement by UV is therefore a primary effect. Thanks, too,
for the reprint on replica plating which I had intended writing
to you fore I think this direct proof of the spontaneity of
bacterial "mutations" is one of the neatest things which has come
out for a long time. As regards the "streptomycinase”", I spoke
to Lightbown as promised but leamed that he had already written
to you directly about it end, since I was busy, I did not bother
to write.

. I heave done a few more things about recombination. The
first is that, in F+ X F+ mates, the efféct of UV on either of
the F+ strains is to inorease its "F value" (as you would say).
The recombination rate rises and -the distribution of marker
characters (Lac, Mann, Mal, Gal, SM) of prototrophs shifts
markedly towards the phenotype of the unirradiated strain which
therefore behaves as if it was relatively F-. If both strains
are irradiated, the balance of phenotype distribution is restored
and the recombination rate is greater than if either mutant alone
is radiated. This, I think, is against your idea that mating
efficiency is a function of the F value differential between the
two partners since, if this was so then equalising the F value

of both strains by treating both with Uv should result in a drop
in recombination rate as egainst that shown when either strain
Glone is irradisted. The second thing is that I have produced
evidence against my theory (which I have no doubt you regarded as
amateurish, naive and altogether unworthy of consideration !) that

/over
—2a

F+ and the mechanism of gene transfer might be identicale UV
treatment of the F+ strain appears to diminish F+ transfer while
increasing recombination rate. Moreover, 5M treatment appears to
lower the rate of + transfer much more than recombination rate.

I h»ve only done one experiment but the reaults seem clear enough.
tlere they ere: :

The mete was 58-151/i"+ X v-677/8"/P— and the duration of
exposure of the "- strain to the Fi, treated in various ways, was
2 hours in nutrient broth. 25 colonies of W-677 were isolated and
tested for #+ conversion from each mixture and, of course, precisely
the same technique was used for each.

F+ culture Noe prototrophs. Percent

treated: F+ conversion.
Nal 122 , 56
UV 60 32
UV + QM (Count rite! 495 4

107%)
In an experiment just cooking I seem to have got 2/53
isolates of «-677/F-, grown overnight in a collodion filtrate
(O'7hp APD) of # young broth culture of 58-161/F+, which have been
converted to Fre An equal volume of filtrate to that in which W~677
was grown was sterile on incubation and no Lac+ colonies were isolated
from ® plating of the test filtrete for J/-577 isolation.

I will have to check up on the converted isolates of
course, and do the whole thing again.

All this makes writing @ discu8sion for a peper very
difficult ‘ ly own feeling is that the process of recombination
is probably unique and, as you wrote me on one occasion, that one
must be guided only by the facts as they come to light. I still
think that there is a very good case for one-way gene transfer,

owever.

Please let me know if you have any good ideas.

With best wishes,

P.S. I am sending a copy of this
letter to Cavalli for his information.

Dr. Joshua Lederberg,
Department of Genetics,
University of Wisconsin, Madison 6,

Wisconsin, UeS-A-