496 DANIEL MAZIA 



but could not be detected in those adult tissues— gut, lantern muscle, and mature 

 testis — which we were able to study. The optimistic view of these results is that 

 the presence of the proteins of the mitotic apparatus is an anticipation of division, 

 that they will be present in cells that will divide in the future but not in cells that 

 will no longer divide. Thvis, they are already present in the ovary, presumably in 

 ripening oocytes, but are no longer present in the mature testis, in which all of 

 the maturation divisions are over for a long time to come. 



A problem which has not yet been resolved satisfactorily is whether the proteins 

 of the mitotic apparatus are related to those of cilia and flagella. The common 

 denominator, of covirse, is the homology of the centrioles around which the 

 mitotic apparatus is organized, and the basal particles of the cilia and flagella. 



Peters ; I find this enormously interesting and it does seem that this conception 

 that Dr. Mazia has given us clears up one of the main difficulties in thinking about 

 the cytomosaic (cytoskeleton), but of course we have still in front of us the awful 

 question as how can this become integrated from the cell surface ? 



Mazia : I would like to have developed a further speculation concerning the 

 paradox of the existence of so much RNA in the mitotic apparatus. We still have 

 no reason at all to think that this structure is concerned with protein synthesis, 

 and we have reason to think that a substantial amount of RNA is associated 

 directly with the protein (or lipoprotein) making up the " fibrous " structure. If the 

 RNA plays a specific or information-carrying role, and if this is not concerned 

 with protein synthesis, I wonder whether we could visualize it as a "recognition 

 RNA". If molecules are to associate with each other to form an orderly structure, 

 we do have a problem, long recognized, of specific interaction or "recognition". 

 One general view of genetic action is that it dictates specificity at the level of cell 

 structure as well as at the level of the structure of enzymes. Could not the genes 

 dictate structure, communicating information as conjugated RNA, to the molecules 

 of which structures are built ? 



Chargaff : Have you examined the reactivity of the isolated fibrous protein 

 with anti-bodies prepared from proteins of the muscle cells ? 



Mazia : We have done the experiments you suggest, comparing the mitotic 

 apparatus of sea urchin eggs with extracts of the lantern muscles of the same 

 species of sea urchin. The results were negative, but could possibly be explained 

 away by problems of diflfusion of the muscle proteins in the agar gels used for the 

 precipitin tests. However, Holtzer and colleagues have obtained negative results 

 when they attempted to stain the mitotic apparatus of chick cells in culture with 

 fluorescent antibodies against chick muscle proteins. 



