March 14%, 195)

Dr. Neal 3. Groman
Department of Microbiology
School of Medicine
University of Washington
Seattle 5, Washington

Dear Dr, Groman:

Thark you for your letter of March 10 which has helped to clarify my understanding
of the diphtheria problem, I will be very happy to see your manuscript and make any
comments that I can upon it.

I would agree, as I have before, on the distinction of this conversion from trans-
duction on the basis of the kind of evidence you mention, namely that "every plaque
forming particle" retains the converting potentiality. I would still like to see an
explicit documentation in the literature on the point that of a sample of survivors of
phage treatment, all of the converted types were lysogenic and equally that all of the
nonconverted types were nonlysogenic. The first part of this statement seems to have
been well established but the second is more obscure but nevertheless necessary,

May I comment on your interest in finding a nonconvertible strain as having some
bearing on the mechanism of conversion, I do not think that the maintenance of cone
verting activity on the part of phage grown on such a nonconvertible strain would be
very decisive, as it would be quite possible for toxigenicity to be controlled by dif-
ferent nonhomologous genetic factors, Such a noneonvertible strain might still vossess
the factors required by other convertible strains, This would be analagous to the site
uation described by Stocker and myself in our work on transduction of motility, of
which I have sent you a reprint,

Your reversion experiments are of course among the most decisive in favor of an
absolute relationship between phage and toxicity. I am looking forward to your pending
manuseript and may I at this tine ask whether you would be willing to vermit me to quote
from it in connection with a review that I will be preparing during the rext 30 days,

On the matter of the discovery of nonconverting phages, while these have « certain
intrinsic interest, I do not agree that they are central to the problem of the mchanisn
of conversion, As you say, it is obvious that conversion is a phage specific phenomenon.

Yours sincerely,

Joshua Lederberg
Associate Professor of Genetics

JL mg