June 17, 1959

Dr. Boris Rotman
Department of Blochemistry
V. A. Hospital

Albany, New York

Dear Borls:
Your letter of May 20th was walting our return from Europe.

We will certainly be what help we can for your problem. |
hope you will find It possible sometime before very long to visit
us and discuss some of the details especially as one of my students,
Ann Cook, Is deeply Involved with the mutants of the Lac region.
Mel Cohn along with the rest of the blochemists has just arrived
and this promises to be an [Interesting place for such studles not
to mention what Pardee Is doing at Berkeley.

| don't think you have yet made a quite sufficient test of the
hypothesIs of galactose as an Internal inducer since even the kinases-
negative strains can synthesize at least galactose phosphate which
might be the Inducer or might be nonspecifically hydrolized to give
galactose. The test will have to made again perhape with a mutant
deficient In the epimerase.

Our "Lac, ‘ mutants have all been obtained by Irradiating
on EMB lactosé agar. About a third of lactose-negative mutants
turned up in thls category. Does the defect In galactose permease
account for the lactose-negative character of these strains?

I will look to see if we have some cultures which carry the
Lac, or Lac, mutation and which are also Gal and should lack
the galactokinase. If we don't have them now it should be no
great trick to obtain the corresponding recombinants, however
as Miss Cook Is taking van Niel's course this summer and | don't
have my own assistant yet, it might take a little time.

Al] best wishes,

Joshua Lederberg
P.S. Thanks for eth reprints; now | can complete the mailings.

It is very odd that Gal, and Gal, should both lack the MGpase; they are
max deficient in the transferase and kinase, respectively, as you know. Have
you looked to see whether MGpase might be inducible by galactose in these mutants?
Galactose might be synthesized through the Galactose-!IDPGal-UDPGIu cycle in the

wild type, and tnis might be a natural inducer in this case. Alternatively
perhaps UDPGal is shexmmux

the inducer, perhaps less likely.
Is there much point in our rushing to send you cultures in Chile? You
indicated you would be returning to Albany in May. | hope we may have some chance

to see you in a leisurely fashion sometime this summer-- perhaps here? Can you

see some way to contrive to travel this way?