February 14, 1952

Dr. JacksonnW. Foster
Department of BacterLology
University of Texas
Austin 12, Texas

Dear Dr. Foster:
In response to your recent request, I enclose cultures of a few auxotroph

mutants. These are all derived from BE. coli, strain K-12 (which has already
been deposited with your colleagues at the Gene Research Group). They are:

W-1834 Cys tinelesa
We1835 "
W-1278 Purineless. [Best response is to hupoxanthine. We do not have

any entirely specific purine matants].

Unfortunately for your purposes, most of our autants are tied up in mlti~suxo-
trophs that woild be somewhat awkward for your needs. For example, Y-53 requires
threonine, leucine and thiamine. Your genetic colleagues would have no trouble
at all in extracting a simple thiamine-less by recombination.

Generally speaking, it is probably simplest in the long run to go after the
particular mutants you need. Present me@Aods, especially the penicillin and
replica-plating techniques, make this task relatively easy.

I hope this limited group of cultures will be of soma use to you. Please
let me know if you encounter any difficulties with them.

Yours sincerely,

Joshua Lederberg
Associate Professor of Genetics