May 8, 19146.

Dear Fyelyn,

I have delayed in thanking you for the culture of B/r to see your paper
in PNAS. I hope you can send me a reprint at your earliest convenience,
Congratulations on a nice piece of work, particularly the ingenuity of your
yethod of double doses, Have you any information on the pessibility of the
mitation from B/r to B ? Have you made any cytological comparisons between
B/r and B? I can't think of any other questions thkt one might presume to
ask relevant to your problem,

The strain we have been using (K-12) dves not seem to behave in this way.
All the mutants in general are survivors of high X-ray doses,xim (with killing
of 1-10 ) but do not seem to be resistant to ultra-violet. Furthermore,
some survivors of a biotinless mutant strain which had been subjected to
16, O00 ergs / mm were no more resistant than the maberadkiont unirradiated
wild type.

Can you calculate the target volume for the division<inhibitpry effect
on the B ? .

We shall probably use this strain for uniformity's sake én our genetic
program, which I think I outlined to you. Therefore any data relating to
the uv or Xeray response, the biochemical or growth characteristics, to
optimal dosages for mutation production, to cytology, etc., would be most
gratefully received. If the publ&hed curves are not qualified, they pro-

vide the most important information. Very sincerely,

Joshua Lederberg

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