FEDERAL SECURITY AGENCY

U.S. PUBLIC HEALTH SERVICE
NATIONAL INSTITUTE OF HEALTH
BETHESDA 14, MARYLAND

 

{IN REPLYING, ADDRESS THE
Experimental Biology
and Medicine Institute April a, 1948

Dr, Joshua Lederberg

Assistant Professor of Genetics
The University of Wisconsin
College of Agriculture

Madison 6, Wisconsin

Dear Dr, Lederberg:

In cleaning up my desk recently, I cameacrose your letter
which you so kindly sent to me some time ago, concerning
reversion in EK, coli, and I noticed yor request in regard
to mutants of strain #58, which I had apparently overlooked
before,

As a matter of fact Howard Mason was mistaken in telling you

‘that I had quite a few of Strain #58 mutants, The mutants I have .
produced in the past have been mutants of E, coli American TypeCutt. Collection
#9723. However, recently we have accumulated quite a few mutants

© of Strain #58, end I have characterized two of these as requiring
pyrimidines, These are very stable with reversion frequencies of
less than 10-9 on horse meat infusion agar. I shall be glad to
send these to you if you should care for them,

Among your remarks concerning reversion you mentioned that
one reversion from lactose = negative to lactose — postive has
been analyzed genetically and proven to be a reverse mutation,
I am assuming this was not done in bacteria, I should like to
have the reference to this work,

I am planning on attending the SAB meeting in Minneapolis from
May 10 ~ 14, and will also probably be in Madison for a short time,
It would be a pleasure to visit you at your convenience,

Sincerely yours,

(34

Robert Guthrie, Ph.D,

—_