.

March 8, 1948.

Up, W. S. Stone,
Dept. of Zoology,
University of ‘exas,
Austin, Texas.

Dear Dr. Stone,

I was giad to hear that your group has so much ag run through the
first steps in recombination experiments with K~l2 mutants. So far as
I am aware, this is the first independ-nt Ngonfirmation", although the
mutants have been widely distributed for 4 long time. I might say that
results come so fast with coli, that there is 4 lot of unpublished data
on segregations of ali kinds of mitants. If anything like that can be
of help to you, please lef me know.

As to your manuscript. I wish that this kind of data had been published
along with your first report, because it certainly mikes Zor a very convincing
case. I can gee no pronounced objections to the conclusion that irradiated
or peroxide-treated broth probably induces “muiations". uf course without
genetic analysis, it is not certain (however likely), as you pointed out,
that these are qualitative changes in individual units, but the same could
be said for ulmost any mutagenic affect on a microorganism. I have a few
co.ments, however, which you may be interested tou hear:

1. From Table 3, it appears that most of the inhibitory effect of
irradia’s broth involves the first two hours after inuculation.Table 1
would have been the more cogent if it had involved comparisons of 0 and 2 h.
Table 3, however, adequately duplicates the results.

2. Your method of testing for mannitol-fermentation is not clear. Do
you use mannitol-agar, and count yellow colonise, or do you pick colonies
to separate tubes. @ am not sure/ that it makes any difference,

3. Frankly, the most objectionable aspect of using drug-resistance
mutations,as I am sure you will agree, is the variability in expression
of the character which is¥f indicated in Table k. You can never be sure tat
you ars ccunting all your/mutaunts, be they treuted or not. On the other
hand, have youbtesated a great many colonies appearing on drug-plates to
ba sure that only mut-ents are counted?

4. During the inhibited period of grath in irradiated broth, do you
get a close correspondence bstween your plate counts and the optical density
¥WeoeStone—2-

of whe cultures. J ask this because it is a nuclear population in which mutations pre-
sumably occur, while your plate count may measure something else.

Have you considered using phage-resistance? That has worked, of course, very well
with E, coli, but 1 understand that irradiated broth has no effect on coli mtations.

- Although these questions couid be clarified, I do not think they are critical
enough to-invalidate your general conclusions. As to your interpretation, I am not sure
that I follow you. The Demerec' delayed effect can still be satisfactorily explained
as a segregation of nuclei or chromatids or whatnot, not to mention phenotypic delay,
Do you still adhere to the statement that specific mutations can be induced by irradiating
particular components? It seemed to me that this was the strangest support of the
"assimilation" hypothesis.

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Thurs sincergly; i

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Noshua Lederberg.
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HAAS F
eWYSS 0 STONE WS—THE EFFECT OF IRRADIATION ON
RECOMBINATION IN ESCHERICHIA-COL! .
P NAS US 34(6):272-239 54 6R

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