Columbia University
Dept. Zoology

44 Nov. 1945
My dear Dr. Lampen,

I hope my rquesta for the pyrimidine-purins strains
did not embarrass you; I misunderstood what you told me about
then at the Protein conference.I hope that you will not
think we unappreoiative of the help that you have given us,
and I cannassure you that I do not want to presse you for a
premature distribution of these mutants.

On the basia of some studies publiehed by Hitohings, I
have been doing a fw experiments with ‘Hydroxy-uracil (180-
basbiturio o0.)* on wild type & coli (ATCC 6532)i These may
be of interest to you:

1. The drug (in the medium used by Tatum & Gray) in-
hibits & coli, primarily by an increase in the lag-time. This
ia quite variable from expt to expt however.

8. This long lag effect is reversed by thymine, and
by uracil,

5. Usacil,but no$ thymine, by itself, shortens the leg

of this wild type & coli in this medium. The relationships of
Sehydroxyuracil to pyrimidines may be useful to you.

Ta re PAB, may I enquire how you datermined contamination
by 4% of your mathionine?

I should also like to repeat the suggestion that a cross-
fesding experinent be attempted. You would inoculate the same
tube whth Pab-less £ ooli and Neurospora, prime it with a small
amount of PAB, and a symsises symbiotic growth of the two would
indicate that different atepea of the spnthssia are blooked in the

tvo mutants.
If you do not have it, I should he happy to send you a transfer of
H. Graaeea 1633 (PAB), which has of course bean published for sone
tine,

While my reagent separation from the Navy (with the termination
of the V-12 program) pute ay ability to continue this research in
&@ Certain doubt, I shall be dalighted te keep you informed of our
results,

Very sineerely yours,

Joshua Lederberg.