UNIVERSITY OF ILLINOIS

DEPARTMENT OF BACTERIOLOGY

362 NOYES LABORATORY OF CHEMISTRY
URBANA

May 11, 1953

Dr. Joshua Lederberg
Department of Genetics
University of Wisconsin
Madison, Wisconsin

Dear Joshua,

I have not heard as yet from Lardy so I guess he still does not know
anything definite about the fellowship. I hope that I will hear soon,

According to what you suggested in our last conversation, I will describe
below the work I would like to do for the first two or three months in
Madison, I believe that after this period, I will find some interesting
project using either some of the ideas you proposed or others that I would
like to discuss with you.

During my thesis work, I found that yeast extracts prepared in a speciel way,
or boric acid to a minor extent, when incubated with yeast cells were capable
of transforming the majority of the cells from salactose-negative to
positive, all the process occurring in the absence of significant growth

(at the most 0.4 generations), The cells used were S, chevalieri which
exhibit the phenomenon of long term adaptation. You might recall that these
cells when grown in absence of galactose lose the galactose-positive
phenotype after seven divisions in an abrupt manner; this we call reversion,
If we accept that this reversion is due to a dilution ,among the progeny ,of
cytoplasmic particles which control the enzymatic phenotype, the reversion
time would be a direct measure of the number of these particles in the cell,
In my experiments, I found that positive cells obtained immediately after
transformation have a reversion time of three genérations, If these cells
are subsequently incubated in synthetic medium containing galactose for about
two hours, the reversion time becomes the normal reversion time of a positive,
that is,seven generations. The interesting point is that these transformed
positives with a full reversion time lack entirely galactokinase (measured

in extracts) and the intact cells are not able to ferment galactose,

I think that this is a very good case of separation of the enzyme forming
system from the enzyme and perhaps it will be a valuable tool to gain more
information about the former. I would like to repeat the observations I have
described to you in a more critical manner and in a similar way for the
galactose-waldenase, By that time we will be familiarized with the system
and its potentialities and we will be in the position to desig experiments
concerning the nature of the enzyme forming system,

I will be glad to hear any suggestions or criticisms you may have,

Best regards to Esther and you,
Sincerely yours,

Rew Ss

Boris Rotman

BR: og