Dear Dr. Rowley:

Professor M, Johnson and I are collaborating on some aspects
of the mechanism of action of penicillin, and it wuld simplify som
of our projected experiments if we could take advantage of some of
the penichllin-sensitive mtants/on which you published a few years
ago. of E. coli K-12,

We would be interested both in your direct selections, and the
correlated-auxotrophic sensitives, and would be mich obliged to you
if you would favor us with subcultures of three or four of them, if
you still have them about.

I am sorry to have missed meeting you during your recent visit to the
U.S. I am sure Tom Nelson feels the same (you may or may not be aware
that he has been back at Wisconsin, in the Botan, Peper tae 2. tis last year.)

i

\ Yours sincerely,
j f

ern ae

| Joshua Lederberg
: Professor of Genetics

P.S. Do you know whethsr your mitants still have the endocellular penicillinase
which is characteristic of most ©. coli strains?