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Defining the Genetic Coding Problem, 1954-1957
Letter from Francis Crick to Jerry Donohue (August 1, 1956)
Letter from Francis Crick to Jerry Donohue (April 28, 1956)
I trust you are now back home safe and sound, and hope that the weather on our east coast wasn't too oppressive while
you were there. I have delayed writing until I thought you'd be back.
I'm sorry that you feel my PNAS paper gives the wrong impression, as I thought I was careful to use the term "polynucleotide"
everywhere except in reference to yours and Jim's structure. You probably recall that just about everything described
in the paper was done while I was in Cambridge, so I was rather amused to learn that Alex (in a letter of last April 18, in
answer to a note of mine about RNA) said he had fussed a bit with the alternate pairings and had come up with the one in my
Fig. 2 at the time your structure was first suggested because "Pauling was very skeptical" (He was at CalTech at the
time, I presume.). How he did this without models I can't imagine. He would like to find a DNA model with mixed right
and left handed turns, to get arournd the uncoiling difficulty, but this looks like a pretty tough nut to crack to me. He
also described in some detail the Rich-Crick-Watson structure for polyA, the one you also mentioned in your last letter to
me. One point I thought interesting, which you didn't mention, was that this single strand helix is, according to Alex,
"a very tight one". Does he mean that there are some uncomfortable van der Waals contacts? Or that there isn't
any large helical hole as in DNA?
After finding the True Solution of the Secret of Life, Gunther dashed off to someplace in the east - perhaps your paths crossed
there, I have yet to hear from him. He and Max Delbruck had been oscillating between here and Berkeley, writing some sort
of phage thing. What he and I have been working on is a two stranded identical duplex (as contrasted to the two stranded
complementary duplex for DNA) as a possible RNA formulation. It makes use of some pairings in the PNAS paper. For genetic
reasons an identical duplex is preferable for RNA, and it looks o.k. structurally - although the determination of a complex
structure with no x-ray data is to me a somewhat peculiar procedure. Since he (Gunther) is leaving for Japan shortly after
he gets back to Berkeley, we really won't have too much time to work this out in as much detail as we would like, but
I wonder if it would be all right with you if you quoted yours and/or Alex's letters, as a private communication, about
your proposed RNA structure in our preliminary note, just to point up the fact that what x-ray data there is apparently indicates
something else. This would keep the biologists from going off the deep end and accepting the speculative as gospel, don't
As for polyglycine, Pauling has been sitting on it, but in the meantime, as you suggested, I think also it is a good idea
for us to exchange results. Dick and I calculated spacings and G2 values out to 25 degrees using your lattice constants and
positional parameters. We get calculated spacings at 4.16, 3.80, 3.10, 2.48, 2.32, 2.13, 2.08, 2.03, 1.90, 1.86, and 1.82
as compared with our observed of 4.15, 3.80, 3.10, 2.47, 2.11, and 1.88. The corresponding values of G2/100 (no temperature
factor) are 72, 14, 66, 27, 11, 15, 22, 1, X34, 53, 9, and 23. Now, we all three shall be most interested in comparing: (l)
how our measurements on the print in "Nature" compare with your measurements on the actual photographs; and(2) how
your calculated structure factors agree with ours. Is there any indication on the photographs of the missing lines at 2.40
2.32, and 2,03? Frankly, it is my feeling that when someone discovers a structure then that one is obligated to disclose
to the world the nature of the evidence for it - even in a note to "Nature", but if for some reason you do not wish
us to discuss the results you send us of your polyglycine results with anyone else, we of course shall not.
Would you please send me also reprints of your paper with Jim, and the one following it, on small viruses. I was rather surprised
to read in it that you had found it necessary to point up the fact that the number of polyhedral point groups - as opposed
to the cyclic and dihedral - was finite (and small), or even that you can't cover a sphere with hexagons, but then I suppose
that the works of Euler and Fedorov are not well known to virologists and their ilk. By sheer coincidence I have for some
months been amusing myself by constructing models of the general and special forms, and their combinations, of the seven polyhedral
point groups. [HANDWRITTEN NOTE: my favorite at the moment is the rhombic triacontahedron] They are esthetically quite pleasing,
and imagine my surprise when last spring I ran across a small-stellated-dodecahedron in Tijuana, made of tin and glass, about
2 feet across, intended for use as a lighting fixture, and very handsome, too. Have you tried, by the way, calculating the
transforms of the general forms of the point groups O -432 or T - 23? It scarcely seems as though you can demonstrate the
presence of a five fold axis by stating that one particular arrangement with point symmetry Ih gives maxima in reciprocal
space in the directions observed, unless you show that this is the only such arrangement that does -- the general forms of
both T and O also have a sort of five-ishness to them, so your argument is actually quite incomplete. By the way, what is
your source for the Hermann-Mauguin type symbol 532 for Ih? I had been under the impression that the numerical point group
symbols had been defined for crystallographic groups only, so it came as rather a jar when I saw that your had included the
dodecahedron and the icosahedron in the cubic system.
We just received a nice letter from Barbara Dunitz, and they seem to be settled in a good location in London, but there was
no news at all about what Jack is doing at the R.I. Today's radio reports that most of southern England is under water
- I hope that there is no serious damage anywhere. Two inches of rain in twenty four hours is quite a downpour, although
last January we had seven inches in the same interval, but then Southern California is used to being washed away every fifth
winter or so.
We have been subscribing to the "Observer" for over a year now, and except when they devote whole issue, as they did
recently, to K's speech, it generally contains more interesting reading matter that the Los Angeles Times, which is at
least twenty times larger in bulk. We were quite surprised to see the small viruses work written up in the "Oberver".
Remembering how DNA hit the "Sunday Times" , please do not let your next field of operations break into the "News
of the World".