J* 13 1946.

Dear Dr. Luria-

   E. coli K-l.2 should 'be on its w?ly in a day or two; I've had to recover it

from our lyophilizsd stocks. While on tb subject, can you tell me what is the

be,& way to put aside a phage suspension for preservation. ive tried to lyophil

T-lin milk without euccese. Can it be dried without inactivationf

  I am preparing to isolate multiple biochemical mutants in B/r per our

conversation last week. However, I must confess that I am a little confused

about the problem ue diacus8ed. As I see it, the inheritance of resistance
can be studied by using biochemical mutants only as the aelective agent for

the occurrence of possible recombinations. The importance of establishing the

separability of the mutations in complex resistance (B/1,6 as compared with
B/1/6) is I think evident. It could be accomplished in two ways:
1. A- X B-/1,6 and isolate from the A+B+typea A+B+/l and h+B+/6
2. A-/1X x3-/1,6           (susceptible;
       and fail to isolate A+B+, isolate A+B+/l, which would support

the alleliryp of the /l in the A- an:: tb B- stocks here mentioned.

Concebab3.y one could isolate using multipk reddance as the selective

agent, but this ia obviowly confused by the occurrence of complex mutations

for phage resistance. Recombination of nutritional requirexnnts should be demon-

strable using them alone as selectors, and only if attempts to obtain them
in this way fail would 1 suggest that it would be worthwhile to use the phags

selectors.  I recall that you brought up another problem, but 1 would appreciate

it very much if you could euimariee it for me.
                         Sincerely yours,

Joshua Lederberg