MOLECULAR CONFIGURATION OF NUCLEIC ACIDS 



which controlled living processes. Research on such matters seemed more 

 ambitious than solid-state physics. At that time many leading physicists such 

 as Massey, Oliphant, and Randall (and later I learned that Bohr shared their 

 view) believed that physics would contribute significantly to biology; their 

 advice encouraged me to move into biology. 



I went to work in the Physics Department at St. Andrews, Scotland, 

 where Randall had invited me to join a biophysics project he had begun. 

 Stimulated by Mullcr's experimental modification, by means of X-radia- 

 tion, of genetic substance, I thought it might be interesting to investigate the 

 effects of ultrasonics; but the results were not very encouraging. 



The biophysics work then moved to King's College, London, where 

 Randall took the Wheatstone Chair of Physics and built up, with the help 

 of the Medical Research Council, an unusual laboratory for a Physics De- 

 partment, where biologists, biochemists and others worked with the phys- 

 icists. He suggested I might take over some ultraviolet microscope studies 

 of the quantities of nucleic acids in cells. This work followed that of Cas- 

 persson, but made use of the achromatism of reflecting microscopes. By 

 this time, the work of Caspersson 1 and Brachet 2 had made the scientific 

 world generally aware that nucleic acids had important biological roles 

 which were connected with protein synthesis. The idea that DNA might 

 itself be the genetic substance was, however, barely hinted at. Its function 

 in chromosomes was supposed to be associated with replication of the pro- 

 tein chromosome thread. The work of Avery, MacLeod, and McCarty 3 , 

 showing that bacteria could be genetically transformed by DNA, was pub- 

 lished in 1944, but even in 1946 seemed almost unknown, or if known, its 

 significance was often belittled. 



It was fascinating to look through microscopes at chromosomes in cells, 

 but I began to feel that as a physicist I might contribute more to biology by 

 studying macromolecules isolated from cells. I was encouraged in this by 

 Gerald Oster who came from Stanley's virus laboratory and interested me 

 in particles of tobacco mosaic virus. As Caspersson had shown, ultraviolet 

 microscopes could be used to find the orientation of ultraviolet absorbing 

 groups in molecules as well as to measure quantities of nucleic acids in cells. 

 Bill Seeds and I studied DNA, proteins, tobacco mosaic virus, vitamin B I2 , 

 etc. While examining oriented films of DNA prepared for ultraviolet di- 

 chroism studies, I saw in the polarizing microscope extremely uniform 

 fibres giving clear extinction between crossed nicols. I found the tibres had 

 been produced unwittingly while I was manipulating DNA gel. Each time 



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