FEDERAL SECURITY AGENCY
WESMINGTON

Tubereulosis Research Laboratory,

Public Health Service,

411 East 69th St., New York 21, N. Y.

January 24, 1952.

Dr. Joshua Lederberg,

Dept. of Genetics,

The University of Wisconsin,
College of Agriculture,
Madison 6, Wise.

Dear Dr. Lederberg:

This is in reference to your kind offer to test
the dominance relationship of penicillin-resistance in K-12.

From your T"LB,” strain W~677, we isolated a
Single—step penicillin resistant mutant. This mutant grows
at a rate comparable to that of its parent on agar plates
containing our minimal medium supplemented with 40 )//ml each
of Di-leuecine and Di-threonine, and with 0.01 ym of
thiamine. The mutant is mucoid on this medium &nd is
resistant to 30 units/ml of penicillin. The parent strain,
after incubation at 35° C for 24 hours, grows microscopically
in the presence of 10 units/ml of penicillin and appears to
be completely suppressed by 30 units/ml.

I greatly appreciate your willingness to do these
tests and I am looking forward to hearing from you when you
have the results.

Sincerely yours,
Henry J. Vogel
HJV/h1

P.S. — We are mailing the resistant strain under separate cover;
it is labelled W-677PR.