November 13, 1952
Dear Mr. Hartmann:
I regret we do not have any mutants of K-12 of the character mentioned in your letter of the 11th.  Like yourself, we would like to have one.  On the other hand, we have frequently isolated lytic variants of lambda which may suit your own purposes.  These variants are readily detected as clear plaques in platings of excess lambda with sensitive bacteria.
The question whether the Lp locus controls the maintenance of lambda, or is the actual site of the provirus in the lysogenic bacterium is one of the greatest interest.  By and large, the evidence seems to favor the latter.
From what can be seen at the moment, the system lambda-2 (the lytic variant) + K-12 (or W-1485) would seem to be as appropriate for cytological comparisons with induction as would lambda + K-12 "alysophoretic mutant".  In either case, you would be dealing with a somewhat distinct chain of host-virus interactions.
Yours sincerely,
Joshua Lederberg