| January 29, 1949.

Dr. Robt. Guthrie,

Exp. Biol. ded. Inst.,
National Institutes of HebAth,
Bethesda 14, -dd.

Dear Bob,

In connection with the work on the heterozygotes in K-12, it has
become desirable to do some outcrosses with unrelated biochemical mtants.
Practically everything we have is derived from the original biotinless
(58 series) or threonineless (673-) mtants which Grgg and Tatun originally
isvlated. Do I recall correctly that you did some work with Kel2 in which
you isolated son: other mutants? I would appreciate receiving whatever
you may have along these lines; it would save us a certain smount of
trouble.

The story on these heterozygotes is vetting to be increasingly com
plicated, but these outcrossesa may help to clear it up.

Thanks for whatever you can do,

Sincerely,

Joshua Lederberg

PeS. Have you ever thought of organizing a conference, under AIH auspices,
on bacterial genetics? iiashington wouldn't be a bad place; or else at the
Cinncinnati SAB. -