January 1}, 1949.

Dr. Fe J. Ryan,
Dept. Zoolagy, ‘
Columbia University,
New York 27, N.Y.

Dear Frahcis:

When I got back to Madison, I kicked myself for having forgotten to
ask you about the discontinuous distribution of mutants in h- cultures,
that you mentioned at Shelter Island. If not too much trouble, could you
tell me whether you have anything new abdéut this exciting finding?

Since getting back, I've received a culture from Cavalli that he reported
crosses with K-12. Like him, I'm having a very difficult job running down
its nutritional requirements; which seem to be for some balanced amino acid
combination, Including at least methionine, threonine, histidine, isoleucina
and valine(but yeast extract 1e very mich better). Anyhow, there is no questdon
that it does cross with K-12, lots of recombinations of unselected markers
having been found among prototrophs, and in additiong at least one hybrid
diploid. But except fob the nutrition, this culture (from the British TC)
is very similar to K-12 (i.e., fermentations and phage responses), and in
fact turns out to be the only other coli strain so far winewiexsmxtaxr tested
that is sensitive to lambda (K-12's lysogenic phage). So perhaps it is only
a "reisolation"” of K-12. But if so, this must be a reasonably common variety
of Coli. On the other hand, this raises the knotty question of what we mean
if we say a coli strain different from K-12, since 1t is reagonably likely
that the species is monophyketic, and that different isolates differ primarily
by a finite number 4f mitational differences. All this by way of answering
the important question, do any strains other than K-12 recombine?

Margaret Lieb more or less casually asked about doing some postdoctoral
fellowship work here. I couldn't encourage her, because all of our space 1s
committed, but conceivably something might break. What would you think of
the idea?

Sincerely,

f,
Joshua Lederberg

P.S. Just géot a letter from Harriett, I was 14tta

she doesn't like sex in coli at all, but perhaps she was juacs littie pet

yore’ by some questions I'd asked about her last paper in J. Exp, Med, leet,
ae JL 4