October 17, 1953

Dear Luca:

I had hoped to defer writing you until I had the time to go
very carefully over our correspondence and set us up to date on the
various interesting points that had come. Unfortunately, I mst inter~
polate another request. I mentioned that W-583 had arrived, broken,
It wad nob recoverable. Can you send me another W-§83 as well as
W-9457 In fact, if it would be convenient for you to send back
any other mitiple-marker stocks I may have sent you before, I think
they should be compared with our present stocks.

Esther and I have had no difficulty comfirming your most interes ting
finding on the linkage of Hfr to Gal (whether Y/¢} Gal, or Gal, is hardly

material!) by prototrophs from M~ Hfr x TLB,- F- “s ant by
a pair of @dY/ Gal+ 3° M. isolated from M-Hfr x M-F-Gal-S° on EYB Gal-sm
As I remenamber Esther's result, there were of course very few Gal+ °

prototrophs, about half or more of them proved to be Hfr when backcrossed
to W-1177 on minimal+ sm. Only 2 Gal+S™ were isolated in the second
experiment, both Hfr; this cross othersise gives only F~{ However,

no evidence for the transduction of Hfr, aldng with Gak+ could be

seen in experiments Gal+ Wéffr —x Gal- F-; Gal+ F+ —x Gal- P+

had been tried before, and the present results were equally negative.
However, as the Gal—transduction system has lately given am especially
competent sub-system, we may try some further attempts, but I am quite
dubious of it. Tom Nelson had previously confirmed Hayes' finding

that F+ x Hfr will give Hfr recombinants when the Hfr parent is effec-
tively F- (viz. subjectei to the aeration phenocopy, while the F+ parent
is treated with streptomycin).

Hayes visited us briefly last month. He is a charming person as
so many people had mkadtx said. But for all of the residual difficulties
with a post~zygotic story of elimination, I am surer than ever (after
talking with him) that the pre-elimination idea will not work at all.

You indicated some doubts about "efficiency&f transfer of B,+ from
Hfr". In Hfr M- x F- TLB,-, on thiamin-minimal agar, I find the sime
ca. 10% B+ as with comparable F+ x F~. Are your data different?
Nelson reports, however, that with Hayes! Hfr (and not ours) the addition
of thiamin has a disproportgonate effect in Ancreusing the apparent
count of recombinants, possibly owing to increased residual growth and
plate fecombination. The cross MF- x TLB_- F+ is giving some unusual
results (almost all B+) not yet fully confirmed.

4a
Helen Byers brought back some very pleasant photographs of tie
Congréss and of yourself; we were especially pleased finally to see these.

Do not feel obliged to make an immediate reply (except for sending
W-583) as I hope to write more later. Of course, I will be pleased to
hear what is going on now that the burdens of the Congresses are over!
Can you tell m the status of our paper on drug-resistance?

I am spending most of my time now on HfrxF- cytology, and am
very discouraged. For a month I could not make again a decent Giemas
slide (g¥/ (1!) but it looks now as if it was only the wrong pH of the
buffer.