Franklin's relations with both Watson and Crick improved greatly once she moved from King's College to Birkbeck College,
and she was in regular contact with both as she worked on the structure of TMV. In this letter, he summarized the work that
Don Caspar had done on TMV, which indicated that the protein was organized around a central hole. Caspar would go to work
with Franklin later that year, and help elaborate the TMV structure further.
Item is handwritten.
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1955-04-09 (April 9, 1955)
Watson, James D.
California Institute of Technology. Kerckhoff Laboratories of Biology
Original Repository: Churchill Archives Centre. The Papers of Rosalind Franklin
Thanks very much for your latest manuscript. For the past several weeks I have been on the East Coast and so out of touch
with TMV. Don Caspar had told me that he would write you, hence the reason I didn't. However upon my return, I find that
he hasn't and so I'll communicate his latest returns.
His sign combination is [diagram], starting at the origin [diagram]. This I believe is quite different from your choice. It
gives a sharp peak at 23 angstroms (which we believe are the phosphates) and another peak around 45 angstroms. It terminates
at 85 angstroms and is almost zero from 0 angstroms to 15 angstroms which we believe is a hole filled with water. He furthermore
has a Difference Fourier (using the same sign combination from his lead [symbol for a positive charge of two] substituted
TMV. He finds that 2 lead [symbol for a positive charge of two] atoms per sub unit (30,000) combine (more [ . . . ] its TMV
is precipate) specifically with the TMV, one at a radius of 25 angstroms, the other at 82 angstroms. The peaks are very sharp,
which he believes is a good indication that the sign assignment is correct.
For the RNA core we favor a 10-12 stranded model in which the RNA chains follow the same helical grid as the protein - This
seems necessary from the perfection of the TMV diagram [diagram]. We like this model since the Cohen and Stanley RNA appears
to have a molecular weight approximately 1/10 that of the [mathematical equation see Lister Hill for tech solution] core.
Under this picture the TMV length of 300 angstroms would be determined by the
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length of the RNA. The problem then becomes to assign a structure to the RNA strands. They must have a slow twist and would
take up essentially a ribbon configuration. To fit these requirement [sic] I have constructed a double stranded ribbon 12
in which the two strands are linked together by pyrophosphate bonds between the phosphates. However it is all very speculative.
Fortunately a chemical test is possible and this we are doing. The main thing in favor of the P-O-P model is that it is very
pretty sterochemically. But does nature always like to be pretty?
I have made an application to the National Science Foundation for a grant to allow me to be in England next year. If it comes
through I shall be back in Cambridge by the first of July. Just recently I have received an offer from Harvard (Asst. Professor
in Biology) and its [sic] most likely that I'll accept. Fortunately they are being very nice and allow me leave of absence
for the initial year. Hence in any eventuality I'll be leaving Caltech in the middle of June.
Hope to see you soon. I'll try to get Don to write you more details