Genetics Department
University of Wisconsin
Madison, Wisconsin

March 9, 195)

ATRMAIL

Dr. William Hayes

London Postgraduate School of Medicine
Ducane Road

London, W. 12

ENGLAND

Dear Bill:

Thank you for your letter of March 3, I was disappointed not to hear more
right away on the success of attempts to separate the i agent from F+ bacteria, but
hope you will have an opportunity to elaborate on this.

I wanted to get in touch with you again right away because I am plarming a paper
to be given in the latter part of April at a symposium on genetic recombination to be
held at Oak Ridge, The report that you have received is more-or-less an gutline of
my own remarks, I wanted to ask you whether youfrould like to make any specific
comment on this story that I would be entirely happy to quote verbatim and o?% course
attribute directly to you. I would not, however, recommend that you include in such
a citation your prediction that the Hfr parent is not going to be recovered from um
selected crosses of the kind your letter mentions, I had studied some several hundreds
of such unselected recombinant containing colomies and it was the presence of the ifr
parent in an appreciable fraction, about 1/5 to 1/3,of these &&& that led me to do
the current single-cell experiments, I wanted to be absolutely sure that the recovery
of the Hfr parent did in fact represent progeny from a single cell rather than from a
pair of cells that night be temporarily stuck together in one way or another, As you
see, the single cell experiment did bear out that presumption, which was however based
on & very extensive series of previous experiments using plating methods,

However, I have been using only the original Hfr strain in all of these experie

ments, Tom Nelson has made a brief examination of your strain in comp..rison with ours,
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' Page 2 -- Letter to William Hayes March 9, 195)

and has found no substantial difference in behavior except for the following: In
crosses of your Hfr strain with, for example W1177, there is in fact a very consid~
erable augmentation in the yleld of recombinants obtained by the addition of Vitamin
Bl to the medium, However, this does ‘ot, as originally might have been concluded,
mean that the proportion of Bl- to Bl+ recombinants is excessive in these crosses,
since when the recombinantsdetected on Bl- containing agar are themselves scored
they are found to segregate about 9 Ble to 1B1l+ as is typical for the other crosses,
We have no explanation for this peculiar effect of thiamine in increasing the yield,
but do not feel that it is based on any unusual segregation pattern of this parent.
For this reason I will be surprised if your Hfr straing shows any different behavior
in crosses analyzed in terms of the unselected zygote. However, do let me know what
your results ars on this point , and if they should prove to be substantially dif-
ferent on the /parent, it will of course be necessary to run a controlled comparison.

I am pleased to note that you are coming around again to a mating interpretation
of E, coli reconbinatdon. I hope some of your many admirers will be as ready to
admit the force of new facts,

I had been confused myself in the past on the formation of zygotes in saline
suspension, Nelson informs me, however, that there is a considerable GREE REAL! DE
difference between the rate of recombination in saline and in the balanced salts
mixture which is the base of the minimal medium, I find in fact that there is as
well something like a 100-1000 fold increase in the rate of recombination in Hfr
crosses conducted in a medium, such as penassay, that permits active growth, as com-
pared with saline or mineral medium suspensions.

To return to your experiment mmber 1, I am a little confused by your reference
tothe absence of reciprocal segregants within individual prototroph containing
colonies, Your previous statement that the Hfr marker S® is missing fromai1l the
colonies would seem to contradict your statement that the reciprocal recombinant
types had been found among other colonies, I assume you mean reciprocal with regard

to some but not all of the markers, I am of course in complete agreement with you on
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Page 3 -- Letter to William Hayes March 9, 195)

the experimental finding that the recombinants tend to be, as I put it in my report,
orthotypic, This does not however/any bearing on the question as to the timing of
the defect which results in this aberrant pattern. With regard to your secon
experiment and the use of phage, I would be interested to learn what the result
would be of a cross reversed with respect to phage resistance, One might be able
to find whether in a cross of F-VyP by F+V,5 all of the zygotes did in fact receive
&hRe a v1 factor from the F+ parent, Since resistance to phage is recessive to
sensitivity to phage, such zygotes would be expected to be sensitive and wiped

out by the action of the phage during whatever interval they were heterozypous,
provided this interval were in fact long enough for the gametic contribution to
become genetically effective,

Yours sincerely,

Joshua Lederberg

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