Dear Dr. Luria-

Double biochemical mitants in B/r have been obtained. Y38-Y43 requires
arginine and methionine; Y39~Y44 requires histidine and p-aminobengoic acid.
However, these mutants do not yield prototrophs when grwon together, nor
when grown with K-12 mitants. Do you want these doubles?

The question remiins whether complex resistance phenotypes occur after
single mutational steps in K~12. Do you have any information on this as yet?

Sincerely yours,

Joshua Lederberg.

wey,