72 



POLLARD: You take out a chunk of cytoplasm? 



MAZIA: A chunk of cytoplasm, that is right. Cells treated in this way have 

 been kept alive for as long as 6 months without dividing. No limit has be en found as yet. 



SPIEGELMAN: Do they keep on making nuclei? 



MAZIA: No, no. 



SPIEGELMAN: But if you amputate just before it divides, then it keeps 

 a double nucleus. 



MAZIA: We don't have any measurements on that. It does not matter. 

 Suppose that it is twice the normal -- 



SPIEGELMAN: It does not matter to me; it might to the ameba. 



MAZIA: The nuclear contents would either regress to the diploid value 

 or remain somewhere between diploid and tetrapoloid. 



SPIEGELMAN: The suggestion then, is that this is controlling not only 

 division of the cell but also division of the nucleus because otherwise the nucleus 

 would keep on doubling. 



MAZIA: Yes, the processes lam speaking of would be controlling every- 

 thing that went into division. That is why lam using the term trigger and implying 

 that the trigger sets off the whole chain of events in cell division, including the nuclear 

 changes. James did a simple experiment. He waited until the cell had begun the mi- 

 totic process. The nucleus was still present, buthe knew the ameba and its history 

 well enough to know that it was about to go into prophase. At this time he chopped off 

 a big chunk of cytoplasm. He could no longer stop division. The cell simply went 

 through with the division and produced two small daughter cells, each with a nucleus. 

 Obviously, the trigger had already been pulled. 



BARRON: The RNA starts increasing only after 10 hours? 



MAZIA: Yes. It begins to increase during the second half of the period bet- 

 ween divisions. 



BARRON: Wouldn't you say that the increase in RNA is the trigger mecha- 



nism 



MAZIA: ItfoUows the predicted patternfor the trigger mechanism. The 

 farthest I would go would be to say that it may be a tracer for the trigger mechanism. 

 It could, for instance, be an index of the multiplication of some cytoplasmic particles. 



CARTER: These are total amounts of RNA? 



MAZIA: Yes. 



CARTER: So that actually RNA could be the precursor, or could be provid- 

 ing parts of the precursor, for synthesis of DNA molecules, and it is only whenDNA 

 has been synthesized and there is no further demand on the precursor that RNA accum 

 ulates. 



MAZIA: The participation of RNA in protein synthesis is by no means ruled 

 out. It is true that cell division takes place between the completion of RNA synthesis 



