I trust that this letter will reach you before the October issue of Journal of Bacteriology. Through some oversight, my paper
on o-nitrophenyl-galactosidase of K-12 omitted a reference to your note on lactase, and your subsequent longer paper in A.I.P.
(which appeared while my ms. was in press). This was not, I think, serious, but I wanted to assure you that it was not intentional.
The paper was written somewhat hastily, about a year after the experiments were completed, and sent off the day I left for
a summer trip to Berkeley.
Not much done on lactase since, except that a mutant has come up which produces lactase constitutively (i.e., in full amounts
on glucose-synthetic medium). Its relationships to Lac- lactase, or to the 7 or 8 Lac- loci are not clear, except that the
"constitutive" mutation is epistatic (as far as lactase) to Lac3-. Esther has been cleaning up some of the loci,
and has indications of even more than those previously listed, although the test for allelism is verified by very large scale
crosses of Lacx- x Lacx- where the identical alleles are extracted from a single mutant source, via diploids, or of independent
Most recently, a large series of fresh isolates of E. coli have been screened for crossability to K-12. About a hundred have
been tested; several cross with K-12 in good yield; a number of others with extremely low yields, but sufficiently to make
it possible to transfer interesting genes to crossable stocks for detailed genetic analysis. Among the interfertile strains
is Escherich's type culture, from the American Type Culture Collection. With one exception, which is intrafertile at
the same low rate as X K-12, I have no information yet on the intra-fertility of the new strains.
May I enclose a request for Doctor Lwoff? We have heard from Ephrussi that UV induces phage-lysis of lysogenic coli. We
have never noticed this with our routine work with K-12, and wonder about the details of the experiment. If we could be favored
with a reprint on this effect, it would be appreciated, as we are anxious to reproduce the experiment. I am sorry we had
no opportunity to compare notes during your visit, as Esther, especially, is working intensively on genetic aspects of lysogenicity