C. Arthur Knight was one of many virus researchers that Franklin visited during her 1954 trip to the United States. A colleague
of Wendell Stanley, Robley Williams, and Heinz Fraenkel-Conrat, he sent her samples of cucumber virus, and in this letter
also addressed questions about the differences between her x-ray diffraction values for TMV composition, and the biochemical
findings by the Berkeley virus lab.
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1954-12-03 (December 3, 1954)
Knight, C. A.
University of California, Berkeley
Original Repository: Churchill Archives Centre. The Papers of Rosalind Franklin
Reproduced with permission of the University of California, Berkeley.
Thank you for your recent letter. We are delighted that you are willing to take a look at the cucumber virus and have enclosed
a pellet of CV4 for your examination. Enclosed also is the sample of iodinated TMV from Dr. F'raenkel-Conrat, who is
writing you about it.
Now I shall try to answer some of your questions. We have actually settled on a number of threonine end groups for TMV which
is different from any of those mentioned in your letter. From careful determinations by three different methods, Harris and
I feel that the value 2900 [plus/minus] 100 per 50 [times] 10 [to the sixth] is the best one that we can get from the carboxypeptidase
work. This is the figure which will actually appear in all our published work, with the exception of the note in Nature.
This, of course, gives a molecular weight for the subunit of about 17,000. This value actually agrees with the one calculated
from the cysteine content even closer than the previous value. Dr. Fraenkel-Conrat has some new data on the cysteine content
which may result in a revision of that figure but, if so, it would be in the direction of making the molecular weight of the
subunit larger rather than smaller; so I am afraid that this is the best we can do with our present data, and I am sorry that
they do not coincide better with your X-ray diffraction data. With respect to the homogeneity of the virus subunits, we can
only say that we have no evidence in our data which would militate against the idea of identical subunits of molecular weight
of about 17,000. The amino acid data would provide for approximately integral numbers of each type of' amino acid residue
in such a unit although it must be admitted that the precision of the amino acid analyses is not good enough to push this
sort of calculation very far. The complete reference to my article is "Advances in Virus Research", Vol. II, pages
153-182, 1954. The paper by Fraenkel-Conrat and binger is in the Journal of the American Chemical Society 76, 180, 1954.
Returning now to the CV4, we should be glad to provide you with more material of a different kind of preparation if that should
seem advisable after you have worked with the material.
It was nice to visit with you while you were in Berkeley and to hear about your interesting work. We wish you the best of
luck as you continue your studies.