a joke, if you under-

*P.S. This is

stand what allelic

means.

*Benzerological
notation.

October 8, 1956

Dear Jacques:

I have waited to answer your request of 3 September for the caari-
fication of some confused data on the allelism of mtants of the
Lac. group. Dr. Newton Morton has been continuing Esther's earlier
work on this, and we would be most happy to have your interest on
the physiological aspects of these mutants. So far, we have concen-
trated on the loci of the Lac, group, but should have more data in
due course on a number of othér mutants» Under goparate cover, I an
semiing you the following collection: (all ate F- prototrophs}

Lac, a W-3230, W-3157, W-3134. These are independent recurrences

so far apparently allelic (1.e., isoritic: rit = recombination unit)
with one another. W-3230 is derived from Y-87; W-3134 from Y-53. W-3157
is new.

Lac,,: W~-3089 (also carries Mal,“S' ) derived from W-112, and equi-
valent to W~2241 which you may have received long ago

other Lac, | (mtually anisoritic)(our notation is not yetom settled)
 We3L48, 3152, 3153, 3174, 3175.

In addition, W-3159 and 3133 are second step mitants from Lac).

The recombination behavior so far is as follows:

(This summarizes theallelic relations; the sequence is being wrked
out now in relation to Ve at the left and P to the right

-

wet eae ee eee uo”

Wr ee ce ne ee ee ent wee tees

_- We_have tentatively defined Lac, as the ispritic projection of W-
° 3229; more study is needed both from the genetic and physiological

side. We would be most immediately interested to learn the quality

The cistronic*relationships are also being worked out; we have the

old datum that la and lb are isocistronic, and some scattered additional
observations. I predict that the whole Lac. group will be isocistronic
but this is not proven. Many of the mutants have been shown to be

both anisoritic and heteroci&éronic with Lac 4°

Rickenberg visited us briefly, and we could discuss some of the

points of your permease work— also with Hal, who finally arrived.

It seams to me the azide effect is still a point of difficulty: when
the inhibitor is used at the same levels as suffice to inhibit the
T™G accumlation, the culture should behave just like Lac, : doubtless
there are mumerous complexities that should not becloud a clear first-
order picture.

Yours sincerely,

Joshua Lederberg