After his return to the United States in the summer of 1953, Watson resumed his investigation of Tobacco Mosaic Virus, the
simple, stable, highly infectious virus that became the standard experimental organism for the new science of virology in
the 1880s. He was interested in the rod-like shape of TMV, whose regular protein subunits Watson in 1952 (while at Cambridge)
had shown to be arranged in a helix. Drawing on the work of Rosalind Franklin (who herself had shifted from DNA to TMV in
1953), Watson suspected that the virus' hollow core was ringed by strands of RNA (as his drawing illustrated).
In his letter Watson reported that he and Don Caspar had determined the molecular weight of TMV RNA to be 240,000 (i.e. 240,000
times the weight of an atom of carbon 12). Molecular weight is a fundamental measure in physical chemistry. Watson also mentioned
other developments in his laboratory at the California Institute of Technology, such as X-ray images of crystals of Southern
Bean Mosaic virus, like TMV a plant virus but spherical in shape (as mentioned in the letter), as well as the acquisition
of an advanced Spinco centrifuge.
Most interesting, Watson expressed his reaction to Crick's RNA Tie Club note "On Degenerate Templates and the Adaptor
Hypothesis," which ended on a discouraging note regarding the complexities of the genetic code. Watson insisted that "[w]e
must find RNA structure before we give up and return to viscosity and birdwatching," their respective fields when they
first involved themselves in scientific study.
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1955-02-10 (February 10, 1955)
Watson, James D.
Original Repository: Wellcome Library for the History and Understanding of Medicine. Francis Harry Compton Crick Papers
I have put off writing because I hoped to be in a position to write a longish letter. First of all, I have done nothing with
the Virus Paper. Reason is preoccupation with many things. However I seem to be returning to work at a steady pace. Visitors
seem to choose this time of year to descend on Pasadena. The following factual information may interest you.
1) RNA -- shows no increase in UV absorption on boiling for one hour (TMV, Yeast, Liver) Nevertheless shows 20 percent rise
when taken from .1 M NaCl to H2O. Have been drawing fibres from some new Yeast RNA of S20 10-12. Seems to behave like previous
samples This is a pity. No x-ray pictures yet, but birefringence and stickyness [sic] seem similar. This should be very clear
RNA so I wonder whether sample improvement will help us. We should probably concentrate on obtaining better photographs from
present samples. Hope soon to get x-ray photos and sedimentation pictures from boiled RNA -- this to check whether specific
hydrogen bonds exist -- would guess they don't. Am going to Berkeley next week to look again for RNA in E.M.
2) TMV Caspar (now here at Caltech) doubts whether Rosy's sign assignment [?] for Equatorials is right. If he is right
in his guesses, we find a high density about n equals 20 PO4?? Probably would pay to talk to her. M.W. of TMV RNA seems to
be 240,000 Are there
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8-10 chains running down the core as follows [diagram]. He guesses low density in the very center; to be expected if the bases
are on the inside. TMV remains the H2 of the RNA world, that is unless PUX is pushed. What about having Roy Markham prepare
you some. --Or is Rosy doing it.
Southern Bean Mosaic: Caspar has low angle curve (Dumond Equipement [sic]) in water and high density salt. First picture gave
approximation to uniform sphere -- second gave nothing. Hence RNA is likely to be highly hydrated.
Bacterial Microsomes: We are preparing them from E. coli for both low and high angle. Since they are 50 td [?] RNA, am curious
whether we shall see RNA powder pattern. Have new analytical Spinco at disposal -- necessary in this work.
Gamow was here for 4 days -- rather exhausting as I do not live on Whisky. Your TIECLUB note arrived during visit. Am not
so pessimistic. Dislike adapters. We must find RNA structure before we give up and return to viscosity and bird watching.
I should like more physical-chemical data before I return to model building -- This we have before summer.
My visit to England: still plan to come by early summer. However certain uncertainties about academic future make simple planning
impossible. Will write when things clear up -- may not be for several monthes [sic]
My visit East was pleasant. Am returning in mid March for several weeks
Regards to Odile -- am looking forward to return to Unit