Genie and Non-genic Parts of the Chromosome 29 



Only one more discussion of the same problem from the biochemi- 

 cal point of view will be mentioned here, though we shall return 

 to it below. Mazia (1952) states correctly that every constituent of 

 the nucleus merits examination as the potential carrier of genetic 

 specificity. He refers to the work of Marshak (1950) on nucleic acids 

 showing that the RNA in the nucleus is chemically different from 

 that in the cytoplasm, and further to the lack of knowledge of 

 whether the RNA of the nucleoli is different from that of the 

 chromosomes (analytical work by Mirsky, Kauffman, and others). 

 Mazia emphasizes that protamine is probably specific for fish sperm 

 with little room left for other proteins; the residual protein (chromo- 

 somin of the Stedmans, 1943, 1947) is found in variable amount, as 

 is the case for the basic histones and a few others. In regard to 

 the quantities of all these, he remarks that it is not very relevant 

 to our problem, since the requirements of genetics are satisfied by 

 quantities below the limit of present analysis. "The chromosomes 

 consist of two major blocks of material; the DNA-basic protein 

 fraction and the residual' fraction containing the insoluble residual 

 proteins and RNA." (I refer here to the later discussions — in the 

 chapter on genie action — of the old ideas, now reappearing, on idio- 

 and trophochromatin. ) Mazia continues, "The former may, in some 

 types of nuclei, be extracted by means of salt solutions, leaving a 

 structurally identifiable residual chromosome [Mirsky and Ris, 1947]. 

 The latter may be digested by pepsin, leaving behind the DNA and 

 at least some of the basic protein, again as a continuous structure 

 retaining the structural characteristics of the chromosome" (Mazia, 

 1941, 1952). The association of DNA with one fraction and of RNA 

 with the other is readily demonstrated by staining and by analytic 

 methods. The relative quantity of the two fractions varies from tissue 

 to tissue within one species. The intermolecular associations of the 

 two fractions as well as of nucleic acid with protein are not clear, since 

 the famous association by salt links does not correspond to the 

 natural condition. Though some chemical suggestions can be made, 

 no real knowledge exists about the natural associations both of DNA 

 and protein and the two main fractions. This is not very encouraging 

 to the geneticist, looking for genetic material with the help of the 

 biochemist. 



Another problem is the seat of the enzymes within the nucleus. 

 Mirsky (1947) found that the phosphatase activity remains with the 

 residual fraction when the DNA-histone fraction is removed, which 

 might mean that the nucleoprotein considered to be genie is full 



