August 26, 1946.

Dear Dr. Sonneborn,

Thank you for your reprints and for the literat&re references
you sent earlier. They me been, need I say, most intereeting.

Nummrous other recombination types have been found in E coli,
corrobarating the account given at Cold Spring Harvour , and supporting
quite conclusively, I think, the hypothesis of a 'sexual' phase.

The recombination types are by no means equally prevalent in mixed cultures,
suggesting that there may be some linkages. “esistance to Tl, thiaminless,
and in other crosses, threonineless have, however, segregated sufficiently
clearly and independently that there mst bed a genic basis to these
characters (andthe others as well undoubtedly).

-e@ are continuing the E. coli wrk, but are studying other bacteria
now as well, having just begun, in particular with Salmonella. In a dis-
cussion with Kimball, the analogy of phase variathon to the self-differen-
tiation of mating types in P, bursaria was pointed out. Do you know =hether
anything has been done since 1942 on that problem? hat do you think about
it? Finally, has any attempt been made to differentiate mating types on a
serological basis?

Very sincerely yours,

Joshua,