CARNEGIE INSTITUTION OF WASHINGTON

DEPARTMENT OF GENETICS

COLD SPRING HARBOR, LONG ISLAND. N. Y.

April 18, 1950

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

Dear Joshua:

Thank vou very much for your prompt and informative
answer to my query.

I agree that it would be preferable to work out the
suppressor story on K¥12, if possible, and your suggested
drug-resistance experiment would indeed be an elegant approach.
I don't think it's altogether impossible to get somewhere
with a nonsexual strain, however. The experiment I have in
mind is to subject a histidine-serine/glycineless "reversion"
to the penicillin procedure, screening for histidineless and
serine-glycineless mutants separately. If a suppressor is
involved, reverse mutation of the Suppressor should release
the two original requirements as a unit, and a fraction of
the histidineless mutants obtained should also require
serine/glycine, and vice versa. Wild type B/r would be used
as a control. Negative results would prove nothing, of
course, but it seems to me that positive results would
establish the suppressor beyond reasonable doubt.

I would appreciate your sending me the K-12 mutanty
requiring histidine and serine/glycine, If it gives proto-
trophs on minimal, or if another K-12 diauxotroph turns up
that does so, I think someone ought to do your drug-resistance
experiment. If not, I will go ahead with B/r.

Thanks again, and best regards to Esther.

Yours sincerely,

Evelyn M. “Witkin