December 31, 1951

Dr. Kenneth 5B. Raper

Fermentatton Division

Northern Regional Research Laboratory
Peoria 5, Wilinois

Dear Dr. Raper:

Thank you for your letter of the 20th, and for the five acténo-
mysete cultures that arrived this noon. Ae we learn something about
the genetics of these forms, I hope to be able to discuss the experi-
ments with you. So far, it is fairly clear that Streptomyces griseus
forms heterokaryons which, however, dissociate gtite readily. The
ordinary procedures of plating out spore suspensions, amd picking
single colonies are therefore likely to be reliable for the purpose
of ensuring initial genetic homogeneity of culturas. tihether more
interesting processes occur (sexuality) has not yet been settled:
some combinations of mutants of 4, grisaas seemed to engender wild
type recombinations; others persistently yielded only the parental
forms. It is this point, and the possibility of “inter-specific"
aseociations that I hope tomexplore further with the cultures provided.

If any obstacles to the application of S. aureofaciens to biological
experimentation exist, please regard that question as closed. I should
be interested to hear your verbal comments, and hope before too long to
accept your invitation to visit your laboratory.

Yours sincerely,

Joshua Lederberg
Associate Professor of Genetics