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DEPARTMENT OF PHARMACOLOGY OREGON 9-3200

NEW YORK UNIVERSITY-BELLEVUE MEDICAL CENTER
NEW YORK UNIVERSITY COLLEGE OF MEDICINE

550 FIRST AVENUE, NEW YORK 16, N.Y.

Dr. Joshua Lederberg
Dept. of Medical Genetics
University of Wisconsin
Madison 6, Wis.

Dear Joshua,

Bernie has 2 pyridoxineless mutants in the W strain which
we are sending to you. 22-99 is accelerated by serine or glycine,
15h-59L is not.I don't know whether or not the B-6 requirement can be
replaced by amino acids, and Bernie(whom I just called about it) doesn't
lmow either.

I have done one penicillin experiment with K-12 to look for
arginine auxotrophs, but didn't get any.sI used W895, W2035, and W677 as
starting cultures. Any arginine auxothophs you have in K-12 would be useful
for us, even if they are blocked in other places, We have one here, K-12-138
which is blocked in carbamyl phosphate synthesis(requires arginine and
pyrimidines), and which we got from Novick.

In regard to different coli strains we have one phenomenon which is
quite curious: we observe the feed-back phenomena I described to you in the
W and the K~12 strain, but not in the B strain. In the B strain, the addition
of arginine to the medium does not depress the synthesis of our enzyme;
and growing an arginine auxothoph in the chemosfat with limiting arginine
does not raise the level of the enzyme.

Thank you for sending me the name and adress of Constance Thomas.
She seemed like a nice person,

Best regards, also to Esther,

yours y
{ wo
vi, eae
Werner Maas
1831-32 One Hundred Twenty-fifth Anniversary 1956-57

A Private University in the Public Service