Madison, Wis.
: February 12, 1952

Dear Dr. Burnet:

I was very sorry to learn that you would once again be uhable to
include Madison in your itinerary of an American voyage. I shall be
most pleased if there should materialize any possibilities of a future
visit of longer duration.

My letter is primarily to ask whether you would be kind enough to
send, or reserge for future shipment, a set of reprints of your papers
with Lind on the influenza virus recombination. I was most pleased to
note that you expressed some reservations about the fluid gene pool
concept of virus recombination; I have (based on my own preoccupations
with ©, coli) always felt this to be an ad hoc hypothesis, not clearly
required by any experiments] result as an alternative to simple or repeti-
tive matings.

You may be interested to learn that the premonitions indicated in your

review with Fenner of the probable utility of immunogenetic studies with
E. coli are being materialized. Dr. P. D. Skaar, who worked with Sonne-
born for his Ph.D. has taken responsibility for this project, using the
thirty odd new, interfertile and serologically distinct strains of E, coli

© that we have recently isolated, (about 2% of the strains testg#ed). So far
the somatic antigens have behaved like any other segregating marker. Very
recently we have also gotten some first clues on the genetic factors con-
trolling crossability, with some evidence of an incipient heterothallic
system.

Curiously enough, Salmonella (typhimurium) has behaved entirely differently
from E, coli. The only recombinationsal mechanism we have been able to find
occurs quite generally among diverse strains, but contrasts sharply with the
sexual behavior of E, coli. Instead, single markers are individually "trans-
duced" by a filtrable non-cellular product, along the lines of the pneumo—
coccus transformation. A great mang mutant factors in several strains have
been tested, and they all work ih the same way. The agent seems to be an
organized, DNAse-resistant particle about .1 micron in diameter; the particles
are not gametes: they carry just one for very few) genetic potentiality of
the parent cell, so that, for example, we do not get recombination of unse-
lected markers. The apparent rate of transduction is limited by the adsorp-—
tion of the agent, and is not more than 1 per 10? cells per marker. The
transductions are not at all strain-limited; probably all the XII-carrying
serotypes (groups B and D) will participate. For exagple the serotypic
#hybrid" 2% IX, XII, i;—- has been obtained several times from S. typhi
treated with the transductive agent from S. typhimurium, and selected in
d-antiserut agat.Mr. Zinder and I have a paper in hand on this work.

@ Even with the delays in surface mail, I trust that you will have
received by now your copy of Papers in Microbial Genetthes, and your
surviving reprint of your 1936 paper with Lush on lysogenicity. Thanks
you very much for your gracious cooperation on this enterprise. I used
the book in my course last semester, and I think it proved quite useful
to my studentsbas well as myself.

Yours sincerely,

 

 s naensensensne