The School of Medicine
UNIVERSITY of PENNSYLVANIA

PHILADELPHIA 4

J a 9, 1951
DEPARTMENT OF BACTERIOLOGY anuary ¥s

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

Dear Dr. Lederberg:

I am at present involved in various problems of tryptophane biosynthesis
in E. colie In part, these studies have included analyses of tryptophane
requiring mutants obtained by the penicillin method with Strain Bs
Depending upon alternative requirements for anthranilic acid and/or
indole as well as chemical analysis of accumulated intermediates, I

have obtained five types of tryptophane auxotrophse Certain genetic
implications which gould not be solved with Strain B have led us off

into isolation of tryptophane requirers of K-12. After repeated attempts
we have but one such mutant. This also responds to indole.

If you have any tryptophane requiring mutants of K-21, we would greatly
appreciate transplants of as many different genetic types as may be
availablee Such organisms will be of great help in our investigations.

Sincerely yours,

et Ses:

a Joseph S. Gots

JSG:dab