Revambar 1, 1956

Dr. P. R. Edwards
Box 185
Chamblea, Ga.

Dear Phil:

ZT am still hoping to hear from you that you can visit us this fall for
two or three days. (I trust you received my letter of some weeks ago, renewing
our earnest invitation). The drskova have been here about a week now, and
are well settled at home end in the lab, in 2 prograg on coli iomunogenetics.
With the use of more sensitive mthods, we are finding thet « lerger and
larger proportion of the serological tyne strains can be croused.

There are 4 number of imuindgenetic problems we are very anxious to éis-
cuss with you at leng$h, and I do hope you will be able to make this trip.

Tino has been following up the genetics of the phese-2 “monophasic mutant"
from M2 (your 53-2034) and we can now give e fairly explicit account of it.
X& stili carries the origins) i and By -2 fs9ters, and undergoss phase
variation betwecn them. Mowever, it aleo carrise = third factor, not yet
nanec so let us call 46 Sphl (suppreesor of phase 1) whose effect is to render
the normal phase-1 ineffective, so that bacteria in this phase sre non-flagellate
wi noneactile, This evidence for thia is fairly good, as the Sphl factor can
be transduced in and out of the stock, and is separsbla from the H, factor
which it mcclfies. By stringent selection with enti-l.< serum, mts tions of
the Sphl factor to the normal condition can bs selected, and normal phase
variation is restored.

This situation 1s very closely similar to what you desaribed for SH#-629 (Selig-
mann's FE. colij~ in fact, in our hands, iientical u: we have not been able to
detect an "1" reaction of the “X" phase, and the cells were nonflagellate. {It
in quite conceivable that under different cozditions or in different media there
would be different degrees of spppression of phase-1]. Howbeit, the genetic basie
of the immotile phase-1 of 3-629 is quite similar to that of 53-2034, except
a) the Sphl factor 1s not precisely identical,w anc the tuo show 4 low rate of
recombination in transduction trials, and b) the Sphl factor of Si-629 rather
more freqoently reverts to give normal 1:1.2 types, such as you already desoribed.

I still haven't gotten around to the papar on the He n° java strains,
but this is only a year overdue.

Sincerely,

Joama Lederberg