During her 1954 visit to the United States, Franklin made many new contacts among the virus researchers all over the country.
Alexander Rich was working on studies of TMV protein that closely paralleled Franklin's and they were in frequent communication
during 1955. Bothered by some measurements he had provided her for an article she was about to send to press, Franklin cabled
Rich to double-check his results. He replied via telegram that he had made an error, and followed up with this letter, in
which he analyzed her latest results in detail.
Number of Image Pages:
2 (137,384 Bytes)
1955-03-24 (March 24, 1955)
National Institutes of Health (U.S.)
Original Repository: Churchill Archives Centre. The Papers of Rosalind Franklin
This item is in the public domain. It may be used without permission.
I am terribly sorry to have made a "butch" in measuring the birefringence of these films. Indeed, the birefringence
is -.002 instead of + .002. This mistake is all the more interesting since the introduction of RNA into TMV changes it from
negative to positive birefringence, while the RNA itself, paradoxically, has a negative birefringence. How can it be that
introducing a negatively birefringent molecule into a protein shell, which itself is negatively birefringent, produces something
which is positively birefringent? Here is a conundrum, indeed.
I found your manuscript quite interesting. I believe that your explanation is correct, namely, that the introduction of further
water into these protein films does, in fact, pull apart the helix so that the repeat distance changes. I think that one
can make an analogy between the photographs which you have obtained at different humidities with the Perutz photographs of
hemoglobin. There, by changing the salt concentration, he was able to move the molecule in and out over different distances,
and was thereby able to sample the transform of one molecule at different points due to the alteration of the latter function.
Here, by changing the water in the nucleic acid free protein helix, one is able to make the helix expand and contract, thereby
sampling the transform at different layer line spacings. The transform in this case is not the transform of the individual
monomeric units, but rather something which is close to the transform of this monomeric unit rotated around the axis. It
seems, from your description, that the protein is able to go from a state which has roughly 37 or so units in three turns
repeating in 68 angstroms into something which has roughly two turns in 45 angstroms perhaps with 25 units or so in this repeat
distance. In other words, small changes in the positioning of the helical coil changes the layer line spacings in this way.
It is apparently just an accident that the photographs that I had have the same spacing as TMV, implying that the protein,
at this hydration packed in a manner which is similar to the arrangement of the protein in the TMV. On introducing more water,
this apparently no longer holds. At any rate, I am going to test this by seeing whether I can take one of these films which
gave me the very bad pictures which you saw here, and finding whether increasing humidity in this film will produce the changes
which you have described. I think that the demonstration of these changes makes the whole problem much more interesting,
in that it produces the possibility of obtaining the complete transform for the cylindrically symmetric monomeric units throughout
reciprocal space in a way similar to way similar to what was done with the hemoglobin.
Newmark has sent me more of the TMV material and I hope to make more films. However, the first batch that he sent me proved
to be unpolymerized, and so I am unable to do anything at the moment. However, I hope to be able to do more work here in
the short future.
My plans regarding the spring are still somewhat indefinite, and I'll let you know more about them later.