CARNEGIE INSTITUTION OF WASHINGTON

DEPARTMENT OF GENETICS

COLD SPRING HARBOR, LONG ISLAND, N. Y.

April 11, 1950

Professor Joshua Lederberg
Department of Venetics
University of Wisconsin
Madison, Wisconsin

Dear Joshua,

Thanks for your early bird contribution for the next MGB.
I will be glad to add the names you Suggest to the mailing list.
I have been putting graduate students on the list if they are
recommended by a senior person as being seriously interested,
so I guess Lively and Zinder qualify. I can see your point
about Gowen's note -- however, he seems quite anxious to
reestablish contact with the bacterial genetics group, and I
thought we could afford to stretch a point so ag not to put a
damper on him. I am entirely open to suggested rules and
standards, and have been thinking we ought to have some sort
of advisory or editorial board. Perhap@ we can get one organized
for the next issue.

What I am really writing about is a point of information
re the stability of polyauxotrophs. I have a strain of B/r that
requires histidine and serine or Blycine, the two requirements
having been tagged on in two steps in the order given. The
first-step strain, requiring histidine alone, has a reversion
rate of the order of 1 per 107, and I was rather surprised to
find that the double-requirer has a reversion rate of the same
order -- if anything, somewhat higher. This, of course, looks
like a surpressor mutation. I wondered if You have come across
this sort of thing in your experience. It's the first time T
have seen it in the course of handling about a dozen diauxotroph
strains of B. If you have investigated this sort of behavior in
K-12, I will not bother with it, as it is a long way from the
current line of my work. If it has not been encountered previously,
it might be worth looking into, if only as a conerete instance
of the dangerous tendency to think of reversions as true back-
mutations without a shred of evidenée. I'd appreciate your
judgment as to whether there would be any point in pursuing this
thing.

With best regards to Esther,

Sincerely,

Evelyn M. Witkin