DeMars was the third graduate student Luria mentored. After receiving his PhD, DeMars took a position at Washington University
in St. Louis. While he was a student at the University of Illinois, the two published several papers together on bacteriophage.
With this letter, DeMars returned to Luria the manuscript by Francois Jacob forwarded to him for comment. He also informed
Luria of some of the results of his continuation of research on bacteriophage.
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Washington University School of Medicine
Luria, Salvador E.
Original Repository: American Philosophical Society. Library. Salvador Luria Papers
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From Phage to Colicins, 1945-1972
Letter from Salvador E. Luria to Robert DeMars (April 22, 1955)
The proofs arrived last week and have been returned. The reprint order is enclosed.
I have been able to get a little work done since we stopped teaching (which turned out to be a much greater [i.e. more tiring]
chore than anticipated). Currently, I am trying to finish up the UV effect on recombination. I got some closely linked r's
(T4) from Berger and found that starting at a control recombination value of 10^3 the value varied linearly with the UV dose
as far as I went (~4 fold increase, P/o ~10^5). This is like T2. Using this pair of r's, the UV increases the frequency
(also the absolute number) of cells which liberate any recombinants at all. I take this as good evidence that UV does not
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Merely cause a selection for recombinants, produced at the control rate, but rather increases the number of recombinations.
I will talk these things over with Seymour when he visits this week. In any event, all I will do along these lines is a few
more crosses of this type and some crosses to see the effect of UV on the number of rounds of mating. I will write a short
report of the findings and stop, since I don't see further development of the work.
Much of these results and those on cross-reactivation would be easier to think about if we had information on the multiplication
of the 'dead' phages per se. I am setting up to see if cells singly infected with UVT2 and P^32 killed T2 can make
DNA with HMC.
We will look for the small amounts of HMC expected by infecting in a medium containing C^14 labeled glucose or acetate and
looking for C^14 in the HMC spot on chromatograms. Probably this will turn out to be mainly a biochemical exercise for me
(eg. Making C^14 glucose), but that is all right, too.
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A further example of my 'diddlings' is my attempt last week to get naked phage DNA into cells. I think it will work
with a little trick to be tried tomorrow. I will let you know if anything happens and only mention it here because at least
someone has tried it. The idea is to try and find out something about the physical nature of the three linkage groups.
I will try to come to Urbana the third week in April on my way East and will look forward to seeing you then. Please remember
me to Zella and to everyone in the lab. We were all sorry to hear of Sol's accident and glad to learn he was back so soon.
I think I will describe the phage DNA experiment in the hope you will have some suggestions to make. The DNA is prepared by
osmotic shock from T2hPf (Pf =proflavine resistant). And is carefully cleaned by centrifugation
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and antiphage serum so that the effects of ghosts are absent and the background of live phages is absolute zero. The preparation
I have has 10^11/ml phage equivalent of DNA and almost resembles egg white in physical properties. I expose B to it at 37
degrees after infecting with T2 T13 at 0 degrees and high multiplicity, to maximize the usefulness of the leakiness of the
cells. After serum treatment I plate the cells on S(2). R13 infected cells do not plate but if the DNA got in (it is r^+)
they might. The check would be in testing any phages for the other markers in the multiply marked DNA. The experiment is spoiled
by the high background of mutants in all my T2r stocks which can plate on S(2). UV'ing them does not help much because
of MR. I am X-raying tomorrow. My T4r stocks have the necessary low background and I will also try these with the T2 DNA.
A success in this experiment would be pretty and I would appreciate anything you have to offer on the idea.