Department of Bact tology,
Postgraduate Medi :
of London, Ducane N,W.12.

Be = 20 Februal

   
 
 
 

f 3

I was most interested to recelve your letter of 16 February
and to learn that both yourself .and Lederberg had arrived at the conclusion
that an infective agent was concerned. Your ‘prediction (and my own!) as

to the results of my experiments on infection were correct. In two experi-
ments,of 25 colonies,all S'az’ picked from plating nixed ,overntant growth
in broth of infertile 58-161/STAzT + fertile 58-161/UV irradiated,7 & 8
respectively recombined with W677. A similar experiment with W 797 gave
10/16 gene donator colonies which showed recombination with infertile
58-161,with which there,was no recombination befere treatment. Incidente
ally,infertile 58-161 behaves ag a "gene acceptor" in a similar manner

to W.677 in that it shows prototroph formation with wild-type, K 12 ang
with 9/10 prototrophs from a (58-161 + W677) mating: the remaining & ;
prototroph.from this mating did not recombine with either W:677 or Fry
infertile 58-161. I had actually started a letter to Lederberg atey
this. when-yaur.letter came. It is rather extraordinary that ‘the: t
of us,working so far apart and presumably from rather different an
(at least in my case)should have arrived at the same broad. eoricltis
I had understood your point about crossing two streptomycin=stert1
strains and had meant to write to you about it this week,to suggest
the following three experiments illustrated diagramatically:

Dear Cavalli,

 
   
 
 
  
 
 
  

(1) PE—> 58-161 @ = S-treated suspension.
OTT n <— or —> = recombination occurs(arrows indicate
W677 W677 probable direction of gene transfer)

Prototroph from. (58-161+W677) mating.
-Recombinatién inhibited.

(2) py SBM <H-58-161 et

 

 

 

3) Bethea fe
& ee ". LI proposed, by using aliquots ,of.the same
SS Weg7F _ cultures of. each of the thhee strains and
_* a ; . doing: everything on the same day,to make. _

 

> ~~. a y=. onditions as comparable. as possible and had
considered giving all the cultures a small dose of UV before dividing. -
up in order. to increase. recombination(without killing a significant _
proportion.of "gene acceptor"cells) and so get. the. most marked differ-
ential effect. | I think I will do this and we-can discuss results, when
you come to .London.. Of. course,I regard the idea behind this as your
own. As regards this "infection" business,it had occurred to me that.
the high infection-rate might be an index of the true recombination. .
rate when all. possible: characters are, taken, into account, the majority
of diploids rapidly segregating out cells resembling the parents in.
reek ee etiy bast number of markers tested fer. normally: recombinat-
ions normally.tested for by a highly selective technique. I have been
struck by the. number of prototrophs. which carry, the. W677 pattern of _
markers,though prototrophs: carrying the 58-161. pattern I have found —
exceedingly: rare. I am not qualified to judge:whether the high infect+
ion. rate is.compatible with infection by a complete gamete. .I do not.
think, that the un-filterability of the gamete(or whatever it is) (To
presents undue difficulty, .I% seems to me:that.4t behaves remarkably
like a phage except that it does not kill or:damage the. infected cell;
The only reason why phages appear in filtrates ts that they lyse the
-eells they,dnfect and so remain: attached only.tq molecules instead of
ito large,discrete: bodies. The K 12 gamete must presumably have .a high.
‘adsorptive affinity for both gene.donator and acceptor cells and would
vtherefore-tend to remain adsorbed to the surface of the former type
of cell after: its extrusion,so. that it could. only be transferred to
‘the latter by contact. I am rather keen on the view that phages.arise
«by ‘mutation. to: virulence from bacterial gametes! I will tell you the
reasons for this(they are slender) when I. see.you.. — am looking _
forward to:seeing you when. you come te Landon. .My telephone number ©
is SHEpherds Bush: 1260,Extension 13. If.I am out. when you ripg,leave_
a telephone number where I ean contact you, .. I have a car and my wife
-and I would be delighted if you would have dinner with us. at our home.
We could talk shop and I cold bring you back. to whereever you are
a “Staying. On-the-morning of Wednesday,March 5 I have an appointment to
. have my Ki2-mutants electron-microphotographed before and -after UV.
Very many thanks for your information about ‘the meeting in Italy.
. ursesiregard it as confidential. . 7

 

‘I shed ,of

oy

 

    

| ORR “Yours sinecerelyy) .),.. 5-: