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UNIVERSITY OF LONDON -

DEPARTMENT OF BACTERIOLOGY.

 

POSTGRADUATE MEDICAL SCHOOL
: OF LONDON) =.- o

POSGRADMED CHISK LONDON DUCANE ROAD
Telephone LONDON, W.12

SHEpherds Bush 1260 (4 lines)
20th.February,1952.

Dear Dr.Lederberg,

Thank you for your last air-letter of January 7,telling
me your findings on the relation of lambda to recombination, which
probably saved me much work.as I would have otherwise have felt obliged

to exclude lambda myself as the agent. Since I do not have any teehnical

assistance this would have occupied a considerable amount of my time,

I must apologise for not having written to you since,but I thought I
would wait until I had some information to give you,and until my reprint:
were ready to send. I now enclose & reprints of the 'streptomycin'
article,together with a typescript of another letter to Nature on the
differential action of UV light. As a result of these findings of mine
I considered it reasonable to adopt,as a working hypothesis,the view
that W677 accepted but did not liberate a gamete while the majority of
cells in 58-161 cultures behaved in the opposite manner. Gavalli's
finding that W 677,unlike K 12(wild type), 58-161 and prototrophs,was
not interfertile tended to confirm this view,as did my confirmation of
Cavalli's finding that prototrophs roving the W 677 phenotype of marker
characters can recombine readily with W 77,and that the fertility of
such prototrophs could be enhanced by UV in the same manner as 58-161.
It seemed to me that interfertikity #@m in gene donator cultures could
best be explained by supposing that a small proportion of the population
of such cultures became gene acceptors by spontaneously losing their
gametes, This appears to happen in populations of bacteria which carry
latent phage,a good example being the reversion of Salm.typhi type Fo
to type Fj through complete loss of the latent phage which appears to
determine the type specificity of Vi antigen,as has recently been shown
by Felix and Anderson. This naturally led to the idea that the K 12
gamete might be an"infective" agent - j.e.a self-reproducing product

of meiosis which existed in the same sort of relationship with the cell
as does latent phage but which dbd@g not disorganise the metabolism of
the cell which it infects. In an attempt to isolate an infertile
strain of 58-161 in order to test this hypothesis,I examined 140 58-161
colonies but all proved capable of recombination with W'677., I then
heard that the same pair of mutants in the possession of Dr.c.C.Spicer
(Central Bublic Health Laboratory, Colindale, London,N.W.9),which had
previously recombined normally,showed no recombination after being kept

for a year on egg medium in the. refrigerator. They behaved as predicted,
Spicer's W677 strain recombining normally with my 56-161,but his
eB 161 failing to form prototrophs with my W 677,even after treatment
with UV. I then found that Spicer's 53-161 behaved as a gene acceptor
in an identical manner to W 677,in that it recombined with wild-type
K 12(using streptomycin) and with all prototrophs which formed
prototrophs with W 677,but not with one prototroph which did not. q
I then attempted to make 58-161/Spicer into a fertile gene donator
by marking it with ST and Azl,growirg it wig in broth with UV-treated
fertile 58-161 and then plating on Sagar and testing 25 STAz! pape
colonies for ability to recombine with W677. I have done this twice
and on each occasion 7/25 colonies have been fertile. I assume that
if the genotype of the two strains had differed these "re-fertilised"
58-161/Spicer strains would constitute recombinants,from which it
might be inferred that the true recombination rate is really extremely
high.. I have also grown W 677/S" with fertile 58-161 under the same
conditions and obtained /8/16 colonies capable of recombining with infertile
58-161/Spicer., I consider this is very strong evidence that the K 12
gamete behaves like an infective agent. I think that the absence of
the gamete in filtrates (or even in centrifuged Supernatants - see
enclosed typescript) can be explained by the fact that the gamete has
the same specificity for the baé¢terial surface as phage has and remains
adsorbed to it after liberation. After all,the only reason why phage
is filterable is that it destroys the cell which harbours it. In this
way contact between a gene donator and acceptor cell would be necessary
for transfer. It may be that a small number of gametes are in fact
-liberated free but cannot be demonstrated by the usual recombination
‘technique. Do'nt you think that this question:‘of filterability might
be approached afresh by the "infectivity" technique which yields such
a high rate of infection? Incidentally,up till recently I have en
‘using logarithmic phase broth cultures of my mutants and usually
obtained a fertility enhancement of X 5 to X 20 after UV. I then tried
ithe effect of UV on overnight agar cultures and obtained enhancements
of over X 200 on three consecutive occasions. I think this must be due,
not to increased UV liberation in old cultures, but to greatly diminished
natural liberation of the gamete. I only have a smattering of genetics
and do not know whether the high "infection" rate and the low normal
recombination rate as tested for by the usual selective techniques are
compatible with the idea that the ‘infective agent is,in fact,a complete
gamete. This is,perhaps,too simple a conception.
‘I fear this is rather a rambling and "wooly" letter but
I find it hard to express myself clearly directly on a typewriter.
I hope to publish some of these results in Nature and then get. down to
the difficult business of writing it up properly and in detail.

With kind regards, ~- Yours sincerely,

* »

_P.S. A letter has just arrived ffémn putin

Cavalli by the afternoon post,telling me- |. .
that you have demonstrated infectivity a (Dr .William Hayes)
months ago! It's extraordinary how these

‘things happen all at once. Please’ let me know

your views about publication. It is interesting that you, Cavalli
and myself,all working from,presumably,a different point of view
should have arrived at the same broad conclusion,