April 14, 1952

Dr. Werner Maas

Toc Research Lab.
411 E, 69 Street
New York 21, N.Y.

Dear Werner:

I am sorry not to have expressed myself more clearly about the
affinities of the Kl and Klt derivatives. That they are derived from
the Wakeman strain seems now indubitable. They differ from K-12 and
sharo with the latter the following traits: the pysogenic phage charac-
teristic of Wakaman, fermentation of sucrose (slow), and according to
yourself, resistance to valine. Esther has managed to transfer the
Waks. phage to K-12, but only with great difficulty. This will facili-
tate a determination of the role this phage may play in sterilitzy.

The negative results to which my letter referred ware those of
crosses of Ki types to K-12. I was repeating your contrast re fertility
of Ki with KLT. However, I found so very few prototrophs even in K1t
crosses that I could not be objectively certain that their absence in
Kl crosaes was not simply a sampling error. It was for this reason that
I askedyyou for your detalis on K1t crosses. I infer that my poor results
with Kit-h2-pl etc. do not specifically conflict with your experimental
findings. We should find common ground whth crossing tests with Kt—p
and K1lt-h2.

I have not had much more luck crossing the polyauxotrophs to other
strains. As I mentioned before, one can get only enough prototrophs to
provide baaely convincing evidence of crossing. Judging from the appearance
of the plates, the Waks. phage may have soncthing to do with this.

If theybwere already sent, the Klt-p and -h2 should arrive ina
day or two. May I thank you in advance.

_ Sincerely,

Joshua Lederberg