YALE UNIVERSITY

DEPARTMENT OF MICROBIOLOGY 310 CEDAR STREET
NEW HAVEN 11, CONNECTICUT

20th May, 1953

Dr. Joshua Lederberg
Dep't. of Genetics
University of Wisconsin
Madison, Wisconsin

Dear Dr. Lederberg,

I learned from Dr. Treffers that
you have been successful in utilizing
resistance to streptothricin as a gen-
etic marker in K-12 crosses, and that
resistance to streptothricin does not
confer any cross resistance to strepto -
mycin. He also stated that the resistance
to streptothricin arises as a single-
step resistance to relatively high levels
of drug.

Since the fermentative markers in
Serratia have proven very difficult to
work with, and since I need another non-
selective marker on one of my parental
strains, I should like to try streptoé.
thricin out with these organisms.

I should appreciate any information
you can give me concerning the genttic
characteristics of the drug resistance,
if they differ from the streptomycin
resistance picture, and also I should
like to know where I might be able to
obtain @ supply of streptothricin for
this work.

This additional nom-selective
marker will permit me to do the critical
experiment of recombination of characters
in Serratia marcescens, which to date is
still hanging in the balance.

Thank y very c

Bile Obl
- Belser

William