CARNEGIE INSTITUTION OF WASHINGTON

DEPARTMENT OF GENETICS

COLD SPRING HARBOR, LONG ISLAND, N. Y.

June 6, 1950

Dr. Joshua Lederberg
Department of “enetics
University of Wisconsin
Madison, Wisconsin

Dear Joshua,

Sorry to trouble you again. I would like to ask you
if you would be kind enough to send me a couple of stocks of
K-12. We need them for a recombination experiment for our
summer course, and I would like whatever strains give the
most clearcut crossing results with the least complications
via syntrophism, etc. Dr. Demerec has a number of your
stocks, and I have run a few classical recombination tests
using W595 and 58-161, and the results were rather messy --
far too much background growth, both on mixed platings and
single platings of each strain. I did not use washed agar, but
I don't see how this can be responsible, as none of our
auxobrophs give anything like this amount of growth under
the same conditions. It is possible that the stocks have not
been carried @refully, but rather than taking the time to
try to track down the difficulty, I thought it would be best
to get fresh stocks, and to make sure that they carry your
certification for giving good clean results, We can, of
course, use washed agar if necessary, but I understood that
good results could ordinarily be obtained without it.

Our experiment will be limited to obtaining prototrophs,
scoring them for phage-resistance and lactose fermentation, and
comparing recombination frequencies with yours, so whatever
strains you send should have these characters as differentiating
markers.

I would be grateful if you could send this material
as soon as possible, as our course starts July 17, and we would
like to rehearse all the experiments beforehand. Thanks in
advance, and regards to all.

Sincerely,

Lely

Evelyn Witkin