26 Nature of the Genetic Material 



long time in the egg without an apparent function. It was thought at 

 first that this might somehow parallel chromatin diminution in Ascaris. 

 But it turned out that the elimination material was Feulgen negative, 

 and recent work ( Ris and Kleinfeld, 1952 ) proved it to be RNA. Thus 

 RNA can accumulate on the chromosomes during oogenesis for an 

 unknown purpose and be thrown off when not needed any more. Ris 

 assumes that the same process might occur in other objects, but with- 

 out visible removal in a body. This shows that there must be room 

 within the structure of the chromosome for large amounts of non- 

 genic material which can be stored and removed. The chromosome 

 thus cannot be a single immense DNA polymer. 



The present knowledge of the chemistry of the chromosome does 

 not help much in understanding the genie material. There is always 

 the objection that we have knowledge only — or almost only — of the 

 chemistry of previously destroyed structures and that conclusions 

 upon the living condition are dangerous. This does not apply, how- 

 ever, to the optical analysis of the chromosome by Caspersson 

 (1939ff.), and it does not apply (or not completely) to results of 

 digestion with different enzymes and direct staining reactions, though 

 such methods are rather crude from the point of view of pure chem- 

 istry. 



We shall consider briefly the meaning of biochemical information 

 for the understanding of chromosomal duplication and for the problem 

 of the genie material in the chromosomes. With the arginine reaction 

 the presence of large amounts of basic protein can be proved after 

 complete removal of DNA by nuclease. This is present in the 

 chromonema within as well as between the chromomeres. The re- 

 action for basic protein increases with the increase of DNA in the 

 contracting chromosome, and it is weakest when the chromosome is 

 devoid of DNA. This conclusion from a staining reaction is, how- 

 ever, not safe; the result may be caused optically by the coiling of 

 the chromonema, as in the lampbrush chromosomes. Serra (1950) 

 states that in the salivary chromosomes the arginine content is high 

 in the bands and low between them, which is in favor of a coupling 

 of DNA and basic protein. In addition to protamine, histones and 

 chromosomin have been found in the chromosomes, and a differential 

 distribution of histones has sometimes been claimed. It would be 

 surprising if other proteins were not present, but it seems that 

 present techniques do not permit going beyond such crude facts as 

 these; moreover, the chemical analysis of extracts has not gone farther. 

 It is possible to digest DNA and the basic protein as well as RNA 



