January 2, 1956

Dear Luca;

I have finally reached a stage in my own affairs when I can
begin to devote real attention to our book. T am very sorry about
my long procrastination, but I have simply been overwhelmed with
other obligations. I hope that this new year will find you in
an equally responsive cfapacity)

First let me make a new suggestion about procedure, It seems
to me that we already havey in our outlines a sufficiently clear
ides of the general organization. Instead of trying to write the
whole book at once in skeleton form, as we have perhaps ween
starting to do, we should do one chapter at a time, as thorouchly
as possible and leave it only when it is essentially done. Then
when all the chapters are finished, we can go back over the cerlier
ones, We cay however, each be doing one chapter at a time, I have
looked over your long~since sent chapters 1 and 2, and feel that
you are getting off to a really good start, Hefore we go any further,
however, I want to ask you if you want to eenmtieocthexmensdtiecom:
prepare one of these (or any other one) in substantially final forn,
as far as you are concerned, so that I can address my comments to
it. Or de you consider that the versions you sent me last summer
should stand for this purpose?

. While I wait to hear from you, I will make what pro,ress T can
in my own first offering, which will be either the "adaptations of
individual organisms" or the "genetic effects of drugs other than
adaptation!,

By the way, I am a little uncertain of the details of now
we agreed to leave the outlines, twe and how the chapters were to
be divided. Could you send me a copy of the revised outline, as you
understand it? I believe we also had a congention about referring
te lines was it to be the distance in em from the first writing
on each page (which wogld save counting lines)?

In the lab, a point of some interest. TI fanally have gotten
around to try to check up on Wollman 2 Jacob, and find that Hayes!
Hfr (which they have been using) has very aifferent proprties from
yours] For example, in crosses of Hfr, x Lae-Gal-S", almost all of
the Lac+S* recombinants are Gal4, while with your Hfr, almost none are,
I have been trying to get at the genetic basis of this difference, but
Hfr;, is in an inconvenient genetic background, and, unfortunately seens=
not to be linked to Gal (in fact I have not been able to zet any Hfr,
recombinants, These comments apply to a By fr ag® s8 "prototroph"
(= W232%) received from Hayes a long time ayo, and evidently the seme
stock as the Pastorians use, The parent M- HfmS" stock, on the other
hand, does not seem to show this remarkable behavior, So evidently, the
Pastorhans are quite right about the high incidence of synzamic induc
tion of Lp+ in crosses with Lp*; this dees not apply to crosses with
your Hfr, and thus we can account for the basic discrepancies, Obvioudy,
Hfriye,g much more nearly resembles the typical behavior of, ey. z. ordi
nary Fy than does Hfr).
Thanks for the redrawn figures; all 4j iff zood order =ere,
: i —_—_—

sor €

/ POPES

& Happy New yeer, fe
P.S. Januaryxt

On rereading this, I see I should perhaps summarize what I had explicitly
asked of you in re the book; 1) Your final version of any one chapter, or
your notice that you consider the previously sent draft to be essentially
final, 2) Yourd understanding of the revised chapter outline. I thought I

had a copy on which was noted a) the primary division of labor, and b) the
revised sequence of chapters, but the paper seems to be lost. We should however
stick to the original sheet for designating the chapter numbers.

I also have another favor to ask of yygg you: One of my new students (who started
last summer), Alan Richter, has been devoting himself to F, and largely the
mechanism by which "motilized" cultures of F+ or Hfr become F-. ((Just before
Christmas, by the way, we acted as human chemostats and transferred a rapidly
groy,gulture of Hfr, at low density in broth, over an interval of about 36

hours, but the results are not yet ready on whether this is a satisfactory imi-
tation of the motility experiments.)) Anyhow, Alan seems to have some propensities
4n this direction for he has already isolated two new Hfr strains, without
especially looking for them; both were noticed after UV for another purpose.

At any rate one of them is highly unstable and reverts frequently to F+, so
frequently that no direct test of its infectivity for F, from the Hfr state, is
possible. (However, most recombinants of the Hfr phase x F- are still F-; while
the derivative F} x F- gives recombinants mostly Fy}, so presumably the Hfr be-
havior is again coupled with non-infectivity.) It just occurred to us that we

(us meaning Alan and me; we = Luca and I) had never thoroughly reviewed the
matter of the initial instability of your Hfr. You have sent me Hfr on two
occasions. The first one I recorded as W-1033, as you may recall. When this

was tested thoroughly later on, it was no longer Hfr, but now Fy. This incident
is the full extent to which I can corroborate the instability of Hfr. The second
shipment of Hfr must have been in early 1953, and recorded as w-1895. This culture
and its derivatives have been studied very thoroughly since then, and their has
been no evidence whatsoever of its reversion to Fi; by motility technique, and
once after uv, F- has been isolated from it (some re-infectable; some refractory),
but no F+ at all, In the JGM paper, you wrote that Hfr had reverted repeatedly.

I would conclude now that the culture changed between about 1951 and 1953 from

a revertible to a stable Hfr., The new unstable Hfr of Richter's would tend to sup-
port this ideas; so far we have not seen any ak stably Bfr derivatives from it,
but we have not had it very long. Naturally, in your efforts to retain Hfr be-
havior, you would naturally select for a stable derivative, if one occurred,

What I want to ask you now is whether you still have your Hfr in its original
gkukieunstable form, or alternatively whether you can give any more details
(perhaps some experimental protocols) illustrative of its former instability
after re-isolation. If you would like, we would be happy to exchange cultures
with you again. By the way, this unstable Hfr also seems unlinked to Gal; a
variety of allelism tests ate being set up/ I am almost ready to wonder if

Hfr is not an ambulatory factor like the Ds/Ac complex in maize, though much
simpler ideas are still possible (I am thinking, of course, of the correlation
with E, as a working hypothesis).

What are you doing in the lab these days? I have had hardly any time for experiments
myself for months, but had been busy in an endless task of developing diploid

stocks for crossing and more pedigrees. This is temporarily in abeyance while I'm
trying to make sense out of the Hfr, crosses, as the high Gal-segregation ratio

has considerable bearing on the technical prohlems of the diploids I am trying

to develop. Otherwise, I am mostly invohed in other affairs in the lab; larry &

Esther 's work on Gal-transduction, for example. Nothing very startlingly new there
except we are beginning to understand why the transductional heterogenotes
("partial diploids" which carry a segregating fragment from the donor) do

not segbegate for Lp as they do for Gal, e.g., in Gali Lp+ --e Gal- Lp*. The
clue we are following now is the fact that this transduction not infrequently
gives an "Lp™" rather than Lpt. We never before understood where the Lpr came
from but attributed it to secondary damage to the prophage. However, in crosses
of an Lpt Hfr heterogenote x F- Lp® Gal-, many of the recombinant heterogenotes
also came out Lp’, (Also, there seems to be a definite coupling ,through the
cross, of the fragment and its corresponding chromosome.) There are two further
clues; 1) the Lp” types are invariably unstable, both for the Lp-phenotype and
for Gal. Where Gal is homogenotic, this can be told by reversions, 2) Although
reorganizations leading to Gal-//Gal- homogenotes, from Gal-//Cal+ heterogenotes,
are not infrequent, Lp® homogenotes have never been seen, To summarize, the Lp*
phenotype never occurs in a haploid; the Lp® never except in a haploid. This
has suggested the hypothesis that the so-called LpT is actually the phenotype
of the Lp® in homogenotic form, i.e., as Lp®//tp®. Unless yop want to invoke
dosage compensation (which is perhaps the same idea) this is not simply a,
matter of Lp® in two doses, for Lp®//Lp® diploids are still senspitive (though
perhaps nad so fully as the Lp® haploid. At any rate, we can explain most of the
results with just one postulate, that the initial product of transduction,
Lp+/ZLp® is intrinsically unstable (and not unlikely inviable, by growth of the
Phage) and must go either to Lp+//Lp+ or to Ip®//Lps , or to a haploid, This
would also account for the moderate percentage of transformed clones (20-50%)
which are not heterogenotic to begin with. We have hopes of testing some of
these ideas by various crosses, but they are almost the first definite notions
(whether right or wrong) of how the prophage fits into the story. We would say
now that the persistent fragments are segnents inclusing the Lpt prophage. In
the heterogenote, i.e., so long as their peproduction is integrated with that
of the bacterium, the whole Gal-Lp complex reproduces chromosome-wise (e.g., in
the induction by UV of a heterogenote to give HFT lambda, only about one phage
particle is released per cell, and this is often effective in transduction). When
the prophage multiplies autonomously, i.e., as a virus, the prophage detaches

so that lytic lambda, e.g., has no transducing activity at all. This, the pheno-
menon bears onjy a remote relationship to transduction in Salmonella. Why non
phage-specific transductions are not alse mediated by lambda, I do not know,

We Jave just lately xmostw received your charming gift, the photographic
portrayal of Italia, and apprdciate it very much.

With the best, as ever,

Sincerely,

Joshua

P.P.S. Jan. 9.
Before I finally mail this, may I ask you about gaur experiments with Ceppelinti:
Did you study the Gal segregation ratios in any crosses of reinfected F~?

Larry asks m to tell you he is furious with you for not answering his letters;
he trusts you will have received the ms. of the first Gal~transduction paper.
(This is due for Genetics, 41:142-156, 1956,Jan.) As he probably told you, he
will be leaving this coming summer to take a position as Asst. Professor of
Biophysics at the University of Colarado Medical School, at Denver. Though he
will be officially in Puck's department, he will actually have an independent
laboratory at the "Colorado Foundation for Research in Tuberculosis!". Actual
they are fine people,it is an excellent appointment, and the connection with The.
is nominal. As they may also be looking for more senior people too, that was
one of the possibilities I had in mind when I asked about your availability.