32 M. H. F. WILKINS 



configuration in nucleoproteins. The diffraction diagram of nucleoprotamine is 

 very similar to that of DNA and it is clear that the DNA retains its configuration 

 when combined with protamine. Nucleohistone in the chromosomes of somatic 

 cells of higher organisms again gives an X-ray diffraction diagram which is charac- 

 teristic of the double helix of DNA; it appears that the protein is rather loosely 

 bound and fills the space between the DNA molecules. In the case of bacteria we 

 have so far only looked at one nucleoprotein which Dr. G. Zubay in our laboratory 

 prepared from E. coll. In that case the X-ray difTraction diagram, which we pub- 

 lished, shows that much of the DNA is in the double-helix form. It also shows that 

 the DNA is largely free from protein. We cannot be certain that some of this free 

 DNA might not be an artifact of the extraction procedure. Dr. Kellenberger has 

 evidence from electron microscope studies on E. coli that the chromosomes in these 

 bacteria may not consist of nucleoprotein, but might consist of DNA itself. One can 

 see the individual threads of the DNA molecules passing through the nucleus. In 

 the case of RNA the same also appears roughly to be true and the diffraction 

 pattern from ribosomes of E. coli is essentially the same as that from a mixture 

 of protein and double-helix RNA. These results have been confirmed by Dr. Klug 

 and his colleagues at Birkbeck College. In many nucleoproteins, and in vivo, both 

 the RNA and DNA have a double helical configuration and the protein is some- 

 how built around them and does not alter that configuration very much. There 

 certainly are exceptions to this rule and there is no double helix, for instance, in 

 tobacco mosaic virus ; there the RNA is a single chain molecule and does not have 

 a configuration at all resembling that of the DNA double helix ; it may be that other 

 exceptions will be found and that the interesting nucleoprotein from tubercle bacilli, 

 referred to by Dr. Chargaff has a special structure. We do know, however, that the 

 tubercle DNA after separation from the protein has the usual double-helix structure. 



