duly 28, 1948.
Dear Luria,

I know that you will be glad to hear that 4 het erogygote has been
found in E. coli K-12. It should be emphasized that such a delay in
the reduction of the zygote is quite exceptional (probably less than
-O1% of the recombinakions) but once agein, this excettion may help to
prove the rule.

Vio 18 @ vary peculiar Tleresistant type. It is sensitive to T5, while
Tl and Tlh form "plaques" which are not jytic areas but regions which
are recognizable as being peouliarly stained on EMB agar. on nutrient
agar, one sees perhaps a faint inhibition of growth. Application of
T1 to Vie does not lead to the devklopment of typical resistents, and
ve is not lysogenic. At ay rete, I was running through a routine

 

1c
test for allelism with the cross: B3- Jace V,* oT,
B= il~ (¥,77)
is

testing the prototropts for Sensitivity to Tl and T5 on synthetic

EMB. Out of more than 260 tests, only one culture vias sensitive to fl,
Since the distinction between the ¥z md Vy, loci woulda depend on this
lone culture, it was purified and retested for sensitivity. All the
cultures tested then were resistant, It turns out that the original
prototroph (¥-465) is sensitive on minimal ager, and is Lac+, but is
continually throwing off pure true-breeding Lac~ and Lac+ segregants
on complete mecium, The Segrugants are of the whole gemut of recombina-~
tion types, including som fe.g. B-M-f-L-Lac-) which are unobtainable
by the oleer selective ne thod. The rate of segregation is so high that
colonies on EMB Lao are thoroughly sectored or mosaio. A few with large

seotors are under study to look for complementary serresante.
As you might imagine, I am worried about being able to keep
this interesting culture, but freqent transfers with concomitant
testing seem to be quite successful for the moment. Of course, some

(segregmts)

' of the recombinants are prototrophs, so that even keeping it on
minimal agar is not certain to succeed. Lyophil may be the answer,
Of course, with this culture, it will be necessary to repeat
the linkage determinations. So far, everything is as it should be,
although my indirect estimate of the absolute distance between (BM)

amid (TL) may be somewhat high.

Of course single-cell tests would be far more Significant here
than they were previously (although the very high xeannk segregation
vate is probably decisive by itself), and arrangements are being made
for these as well as for cytologtoal study. Just offhand, there
was no particular sign of filamentous forms, in a simple smear.

So far everything points to the delay in reduction being an une

predictsle accidamt, but now that 4t is clear what to look for, a
closer scrutiny will be made.

As you requested, I sent a batch of cultures to Miss Zann quite
some time ago, but theye were mysterianmly lost; however, she wrote
that the second batch just sent have arrived,

Kote the sugee stion above that phage-resistance is recessive. I
an quite convinved that the delayed effect is a segregation, probably
ef nuclei.

I am writing in mich detail to you becaise I owe, in part, my
attention to the possibility that W-465 txmxkbewas zygotic to thinking
generated by your criticisms ak Minneapolis.

With best regards,

Jqsma Lederberg