UNIVERSITY OF LONDON

 

POSTGRADUATE MEDICAL SCHOOL
OF LONDON

Telegrams

POSGRADMED CHISK LONDON DUCANE ROAD
Telephone
SHEpherds Bush 1260 (4 lines) LONDON, W.12
Department of
Bacteriology. .

end April, 1952.

Dear Cavalli,

I would be very grateful if you could send me your radiation
resistant 58-161 strain which shows increased recombination rate.
I am anxious to try and determine whether the enhancement effect
of UV is secondary to lambda phage liberation, as suggested by
Lederberg, or is a primary effect. For this purpose I want a
lambda-free 58-161, and it occurred to me that your eerne resis-
tant strain might be suitable, smc om yuk nope radiatron-

. abecting P fac atroain ooorn Gpetgein s eects a 6 pied Aowtilbhorn-ruschenlt re etosiice,

ave dorfe s more experiments since I saw you and think

I have now pretty good evidence that the fertility factor (F+)
does not simply confer compatibility between otherwise equivalent
strains, but that, in fact, "gene donator" strains lack the "Gam-
ete" and therefore are capable of receiving it and that the essen-
tial function of F is connected with infection of F- strains with
the gamete. .

According to the self-compatibility theory, maximum recombin-
ation should occur between F+ strains as these strains are already
fully compatible. On the other hand F+ x F- matings should, if
this theory is correct, occur in two stages: (1) The conversion
of the F- strain to F+ and (2) The recombination between the now
compatible parents. These matings should therefore be less
efficient that F+ x F+ matings.

; . /According to my theory
According to my theory however, since F- strains consist
exclusively of "gene acceptor" cells, matings of these with
F+ cells should show maximum recombination. On the other hand
since F+ x F+ matings (according to my theory) will depend on
the presence of a small number of “gene acceptor" cells in tie each
population which have spontaneously lost their “gamete” this
mating: should be minimal.

I have carried out carefully controlled quantitative estim-
ations of the recombination rate with F+ x F+ and F+ x F- mixtures
of the same strains under identical conditions and find that the
latter combination is about ten to twenty times as efficient as
the former.

I don't know whether I have expressed my meaning very clearly
in this letter but I ho e shortly to send you details of these

i erperimen tay aa wrk a Rat cugyeetec! fOr on ei foiling Fix Fr
cto Cock patrinsen Yours nine,
athol uordk Mpg

Dr. L. Cavalli, a

Instituto Sieroterapico Milanese,
Milana,
- Via Darwin 20, Italy.