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The Rosalind Franklin Papers

Letter from Rosalind Franklin to Robley Williams pdf (100,158 Bytes) transcript of pdf
Letter from Rosalind Franklin to Robley Williams
Robley Williams was one of many virus researchers that Franklin visited during her 1954 trip to the United States. He had written to her about her recent article on the probable structural configuration of TMV, as revealed by x-ray diffraction studies, and mused about the differences between her data and those found by he and his colleagues via different methods. In this letter, she responded to his comments.
Number of Image Pages:
2 (100,158 Bytes)
1955-02-14 (February 14, 1955)
Franklin, Rosalind
Williams, Robley
University of California, Berkeley
Original Repository: Churchill Archives Centre. The Papers of Rosalind Franklin
Reproduced from the Franklin Collection at the Churchill Archives Centre with the permission of the copyright holder.
Medical Subject Headings (MeSH):
Tobacco Mosaic Virus
X-Ray Diffraction
Exhibit Category:
Envisioning Viruses: Birkbeck College, London, 1953-1958
Folder Number:
Unique Identifier:
Document Type:
Letters (correspondence)
Series: Work on Tobacco Mosaic Virus (TMV)
Folder: Correspondence Relating to Franklin's First Visit to Berkeley, California, Mar. 1952 - Mar. 1958
14th February, 1955.
Dear Dr. Williams,
Thank you very much for your letter of 6th January.
Of the two difficulties which you mention, I find the hexagonal platelets rather more disturbing than the density considerations. I don't think the X-ray results are consistent with a helical rod of hexagonal cross-section. I suppose it is possible that the stable configuration of a very short length of the rods is different, and that some re-arrangement may therefore occur when it is broken off. Alternatively, if the virus is of a well-defined length, the ends presumably differ in some way from the rest of it so could the hexagons be the end-pieces? I don't think either of these explanations is very satisfactory.
The calculated density depends on the accurate knowledge of the diameter. Bernal and Fankuchen's figure was 152A, not 150A, and this reduces the density from 1.52 to 1.48 s/cc. Pirie has always emphasised, in discussion, that his preparations have been inundated in commercial trypsin and therefore differ from most other preparations and, in particular, may have lost something from the surface. The diameter need only be increased to 157A to reduce the density to 1.38 s/cc.
Again, if I am right in thinking that a helical groove is an important feature of the structure, then for an inter-particle distance of say, 152A, the volume of the particle may be slightly greater than that of a cylinder of diameter 152A, owing to inter-locking of the grooves of neighbouring particles. But this effect is unlikely to be greater than about 2%.
So although the observed and calculated densities cannot be said to agree, I think the diameter and shape of the particle are probably sufficiently uncertain for this not to be too serious.
My measurements suggest that the groove may have a depth of as much as 20A (with pitch 23A). Would you expect to be able to detect such a groove in the electron microscope? I don't know anything precise about its contour, except that it seems to be such as to allow inter-locking of neighbouring particles.
With best wishes,
Yours sincerely,
Rosalind Franklin.
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