June 26, 1952

Dear Pontecorvo:

I should be# very glad to talk with Roper: I have followed the
work you two have been doing with the greatest interest (but have scme
reservations as to whether any organism which displays recombination
{fs still asexual.)

The lab. is likely to be a bit crowded, and I have other commitments
for visitors and students next year. Until Roper'’s plans are a bit more
definite, I won't be able to tell for sure whether he can be accomodated,
but will be glad to discuss 1t with him at any time.

There is a potnt of technique in the Aspergillus work I don't quite
understand.When conidis. from balanced heterokaryons sem treated with
camphor are plated on minimal, diploid proteotrophs are selected. If one
did this sort cf experiment with Neurospora, all one could see would be the
resynthesis cf heterckargons. How can this be avoided-~ or is anastomosis
much rarer in Aspergillus than in Neurospora?

If you get hold of the 1961 Cold Spring Hurtor Sypposium , very
recently in print, you muy be Interested to see the account of pseudvallelism
in E. coli K-12, for factors controlling lactase production. We did not go
into it very deeply, but could find nv biochemical distinction bedbech the
acticn of the pseudoalleles, although another quite closely linked factor
(Lac,} was distinctive.

Sincerely,