UNIVERSITY of PENNSYLVANIA

PHILADELPHIA 4

The School of Medicine

DEPARTMENT OF MICROBIOLOGY
October 30, 1952.

Dr. Joshua Yederberg
Department of “enetics
University of “isconsin
Madison, Wisconsin

Dear Lederberg:

I have delayed answering your inquiry concerning lysogenicity
in E. coli B because I kept hoping that each day I would have something more
definite to tell yous We have isolated, on several occasions, phage from
plagues obtained by plating E. coli © on K-12 or W-1485. Unfortunately, these
occur in very low frequencies with poor reproducibility. We are quite convinced
that E. coli B, or perhaps mutants of B, can form plaques on 4-12. However,
the ability to show this has been quite sporadic and elusive. We hope to event-
ually determine the optimim conditions, one of which at present appears to be
a regime of starvation. We also are ever aware of the technical possibilities
of a contamination with a lysogenic strain. As soon:as we can reproduce this
at will I shall let you know.

We too have found that the W strain is lysogenic producing several
tyoes of phage, one of which plates on K-12 but not on a wild type which we
obtained from clinical sources (WM-13); the other plates on WM-13 but not on
K-12.

bob Guthrie tells me that he obtained one of your purine requiring
strains from Bernie Davis which grows in guanine but not adenine. This is not
a usual occurrence. I am particularly interested in the purines and pyrimidines
and would greatly appreciate any of your mitants which show requirements for
these substances.

Sincerely,

JSG: jlh