Jane Ds 19 48.
f fa
Dear pave, Jarre

While continuing the genetic work on E. coli (and waiting for
Warburgsg Spectrophotometer, etc. to do the physiological) Itve
gotten under way with Salmonella, In the first mutant run, with
S. typhimurium, a mutant was picked up that you might be interes-
ted in. It requires isoleucine and valine, anc with the propor-
tions used (===) is strongly stimulated by additional leucine.
Unlike E. coli K-12, S. typhimurium is not inhibited by valine.

As far as I have studied it, the mutant (SW-7) is quite enalogous

to Weurospora 16117. Would you be interested to have it? The bug

is only mildly pathogenic to mam, bahaves like coli in culture,

and the only precautions that need be taken are a) not to swallow
the cultures and b) to sterilize glassware used with it efterwards
either in the sutoclave, or more conveniently for pipettes in a jar
of lysol. My sole interest in it is to learn what proportions of

the amino acids will be optimal so that I can well use it for the
production of double mutants. The other mutants so far are & trypto-
phaneless (anthranilic inactive; indole slightly active) and a his-
tidineless. There is also a pab-less which needs something else also,
ane a yeast extract mutant (NaCase + Vits., YA, Purines + byrimidines
are all inactive).

With kats departure, we shall have to come to some decision as
to the exchimge of cultures. Shall I continue to send my most interes-
ting streins for deposit and lyophil with you, or would you prefer
that I merely inform you what I have so that you can write for any-
thing you'd be specially interested in? By the end of the year, we
hore to have a lyophil apparatus in operation here, but until then
the preservation of cultures continues to be = mild headache.

Itve received Dr. Sinnott's letter concerning the Genetics of Micro-
organisms, Thanks for the boost. I haven't answered it pending a
decision as to the best time to come, but probably early in November
will te our best bet. Whom else do you have in mind for the lectures?

I've been pleying around with Burkholder's subtilis mutant: the
last couple of weeks , but the answers so far are quite equivooal.
I'll let you know when I have some drug resistance markers put on
the stocks.

Sincerely,

Joshue Lederberg.

P.S. Ed and you may be interested to learn that Szilard & Novick, at Chicago, re-
peated some reverse crosses involving V, and Ve» and oame out with a very neat and
quantitatively precise confirmation. .