Genie and Non-genic Parts of the Chromosome 27 



and the residual protein ( chromosomin ) without destroying the 

 structure of the chromosome (see Mazia, 1952). However, Serra claims 

 that the decomposition of salivary chromosomes in alkali proves that 

 a continuous core of non-basic proteins is present in the chromonema 

 and thus also in the chromomeres. It is the basic protein which is 

 supposed to be linked by salt Hnks with the DNA in the chromo- 

 meres. Serra calls this the "peripheric nucleoprotein" and considers it 

 as identical with the kalymma of the morphologists; he concludes 

 that only the chromonema (with its mostly non-basic protein) is 

 responsible for genie activities, while the peripheric nucleoprotein 

 is important in cell physiology. Thus, on the basis of a chemical 

 investigation of the chromosome, he arrives at conclusions which are 

 rather different from those of most cytologists and geneticists. This 

 is partially compensated because he thinks that, at the time of 

 redupHcation of the genes, the nucleic acid surrounds the genie 

 chromonema and produces a passing nucleoproteinic structure of 

 the genie material. This interpretation can be easily brought into 

 Hne with the results of our former discussion, based upon chromo- 

 somal morphology. The same is true of Serra's (1947) statement 

 that it is expected, in view of the diversity of genie actions, that 

 the pure chromonemata consist of many proteins and polypeptides. 

 The extraction of only one protein, say chromosomin, means that this 

 is no more than an oversimplification owing to the absence of more 

 refined technique. (Further, not very helpful details can be found 

 in the reviews by Mazia, 1952, and Alfert, 1954.) 



From such chemical and positional facts, Serra derives further 

 ideas on the physicochemistry of the chromonema, though the direct 

 attack has not provided much information. The chromonema can 

 be stretched immensely in the already stretched salivary and lamp- 

 brush chromosomes (Duryee, 1937; Buck, 1942), up to three to five 

 times its length, which must involve molecular unfolding. The 

 chromosome as a whole is a special kind of fiber in which the pro- 

 teins are disposed as if they were semiglobular and semifibrous units, 

 in a sequence similar to that of the genes. The proteins are folded 

 in a visible helix ( spiralization ) , and more or less similar foldings 

 exist also at submicroscopic levels, down to the molecular looping 

 which must be similar to the folding of globular proteins rather than 

 to the more or less straight disposition of the polypeptide chains in 

 fibrous proteins (Serra, 1947). A chromonema, however, is not a 

 single protein chain but a bundle composed of from 10^ to 10^ indi- 

 vidual chains, according to Serra's calculation. 



