ir ORGANOGENESIS 729 



b. Cytological mechanisms. Biological studies have followed essentially three lines 

 of approach: (j) incorporation of labeled amino acids, (2) adaptive enzyme 

 formation and, (j) nucleic acids in relation to protein synthesis. The evidence for 

 association of RNA, particularly of microsomes, with synthesis of proteins seems 

 overwhelming (Caspersson, 1947; 1950; Brachet, 1952; Hultin, 1950a). Gale and 

 Folkes (1955a) find that disrupted Staphylococcus aureus cells incorporate ''*C 

 glutamic acid in the presence of ATP and hexosediphosphate as energy sources; 

 the rate of incorporation is enhanced by nucleic acids. The same authors (1955b) 

 studying specifically enzyme formation show that when cells are partially depleted 

 of nucleic acid, restoration of synthetic capacity can be accomplished by RNA or 

 a mixture of purines and pyrimidines; however, when nucleic acids are severely 

 depleted, DNA must be supplied, as well as RNA and purines and pyrimidines 

 in order to restore maximal synthetic capacity. Brachet (1952) summarizes the 

 apparent present status of the question as follows: protein synthesis may be due 

 to the direct intervention of microsomes, and multiplication of these particles is 

 under nuclear control. The role of the nucleolus, although probably significant, 

 is not yet completely clear. The method by which the RNA of microsomes 

 participates in protein synthesis is still a matter of speculation, whether by an 

 indirect function or by serving as a "template". 



Details of relationship between RNA and amino acid incorporation are 

 becoming more clear by virtue of persistent work in several laboratories. Many 

 features of this are summarized in a symposium of the Biophysical Society (Roberts, 

 1958). The mechanism appears to be enzymatic amino acid activation in the 

 presence of ATP, attachment of the activated amino acid to soluble, cytoplasmic 

 RNA, transportation to microsomal RNA. Peptide linkage formation and 

 separation from microsomal RNA are not as well understood, but these are the 

 essential, final steps. {Cf. Zamecnik and Keller, 1954; Hoagland, Zamecnik and 

 Stephenson, 1957; Berg, 1956). 



c. Relationship with yolk storage. The problems raised by Fruton would appear to 

 bear particularly on questions of maintenance; although the processes which he 

 describes may not be eliminated from embryological consideration, almost 

 certainly in yolk-bearing eggs they must be supplemented. We have reviewed 

 above a substantial literature leading to the conclusion of identity of some 

 adult and egg proteins, and have described a plausibiHty for the incorporation 

 of intact protein molecules in the developing embryo. There is not yet ex- 

 perimental evidence to suggest that all adult proteins are deposited in the 

 egg, and it would appear unnecessary to suggest such preparation of the egg. 

 Such a view is at once prejudiced in favor of the notion of "template" 

 activity, but rather than answer significant questions it raises new ones with 

 respect to the assortment, or delegation of, peculiar proteins to their appropriate 

 tissues. 



It is an inevitability that limitations on the synthetic ability and selective 

 permeability of the ovary require that only certain of the adult proteins become 

 incorporated in the egg. But the epigenetic development of the embryo entails 

 the appearance in its structure of some devices which have only local applicability, 



Literature p. 744 



