94 CONTROL MECHANISMS IN CELLULAR PROCESSES 



the account respective volumes, show that about twice as much is 

 formed in the chromosomes as in the nucleohis. Woods (1959) 

 came to a similar conclusion in his experiments with roots of Vicia 

 faba. 



The nucleolus in the salivary gland preparations used for auto- 

 radiography is not easilv distinguished from the chromocenter and it 

 may be that the high synthetic activity of the nucleolus is actually 

 due to the heterocliromatin of the chromocenter. Felling (1959) 

 and later Sirlin ( 1960 ) showed in different Chironomidae that the 

 nucleolar RNA appears first in one side of the nucleolus only, the 

 part which is closest to the supporting chromosome. No such re- 

 gional RNA formation could be observed in our preparations, since 

 in one minute the nucleolus was radioactive throughout. 



A few other cells synthesize RNA fast enough to allow detection 

 of newly formed RNA after very short time intervals. Active RNA 

 synthesis can usually be found in ovocytes. In Drosophila, nurse 

 cells take over the task of RNA synthesis and it can be shown that 

 newly svnthesized RNA accumulates quickly inside the nuclei ( Zalo- 

 kar, 1960a). Unfortunately, the nuclear structure of Drosophila 

 nurse cells does not allow an easy distinction between the nucleolus 

 and the chromatic material in autoradiographs. 



More favorable are the panoistic ovaries of more primitive insects, 

 as found in the order of Orthoptera. Cockroach ( BlateUa germanica ) 

 has large ovocyte nuclei with beautiful nucleoli. Egg production is, 

 however, slower than in Drosophila, so that longer times are needed 

 to detect incorporation of precursors into RNA. I wish to report 

 here a few unpul)lished experiments with BlateUa. The ovaries of 

 cockroaches which were still carrying the egg case with the previous 

 batch of eggs, were incubated in vitro in H" uridine-containing physi- 

 ological solution. They were fixed 4 minutes, 16 minutes, 1 hour 

 and 4 hours later ( Fig. 4-1 ) . In 4 minutes, no incorporation could 

 be detected. In 16 minutes, the nucleoplasm, containing "lamp- 

 brush" chromosomes was labeled, the label was especially evident 

 over the chromosomes. The nucleolus was only slightly labeled. 

 After one hour, the nucleolus became labeled, but only on several 

 spots of the nucleolar peripherv. After four hours, total labeling of 

 the nucleus was much higher, and the nucleolus became labeled 

 throughout, indeed more than the surrounding nucleoplasm. These 

 preliminary results appear to show a chromosomic synthesis of RNA 

 and a migration of RNA from the chromosomes to the nucleoli. 



