Department of Biology
University of Rochester
Rochester, New York
Decemfer 12, 1955

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

Dear Dr, Lederberg,

As a graduate student studying transformation of Pneumococcus under Dr.
Ravin, I have become interested in the possibility of transforming other
bacteria, particularly E, coli, K-12. I have a procedure outlined which
should detect mutants to transformability, if such occur, even at relatively
low rates. The system requires the use of a polygenic quantitative resistance
to a selector. If the Cavelli-Maccacaro observations on the quantitative
character of chloromycetin (chloramphenicol) resistance are correet, this
would be an ideal selector to use. For this purpose I would like to obtain
a strain of K-l2 resistant to chloramphenicol at concentrations of o40-1280
micrograms/ml, If you have such a strain available I would greatly ap-
preciate obtaining it.

Sincerely,

am ar ell V) \. wes

i t

Donald M. Green