TABLE II 

 The Effect of Actinomycin D on Lens Protein Synthesis in Calf Lens Epithelial and Fiber Cells. 



POLLARD: How can you avoid having that 

 happen if the t-RNA is there? It seems to me 

 you've got to have some stimulation if there is 

 a long-lived message present. 



GROSS: We reported, in 1962, stimulation 

 by actinomycin in the sea urchin and we sug- 

 gested that it was the sparing of ATP. 



PAPACONSTANTINOU: Tomkins and his 

 coworkers have recently presented their ob- 

 servation on the stimulatory effect of actino- 

 mycin on liver enzyme activity. They have 

 shown that the induction and early periods of 

 enzyme synthesis are inhibited by actinomycin 

 whereas after a given period of time enzyme 

 activity is stimulated by actinomycin. They 

 believe that at the time these enzymes are 

 stimulated by actinomycin their m-RNA is 

 stable and a repressor is inhibiting further 

 synthesis of this m-RNA. The stimulation occurs 

 only when actinomycin inhibits further synthe- 

 sis of the repressor. Pollock has also shown 

 a stimulation of penicillinase by actinomycin in 

 B. subtilis. He also showed that ^-galactosidase 

 is not stimulated. One of his explanations for 

 this is a difference in binding of actinomycin 

 to the bacterial genome, thus explaining the 

 differential sensitivity of these two enzymes 

 to actinomycin. He proposes that this differen- 

 tial binding of actinomycin may be a function of 

 the GC content of the individual genes. 



GROSS: That's a fine idea if you can show 

 that all the RNA synthesis is lost. Pollock used 

 very low levels of the drug and he did not 

 present fully convincing evidence that he had 

 shut down all synthesis of template RNA. 



PAPACONSTANTINOU : Well, it didn' t mat- 

 ter whether he shut it down or not. He showed 

 he got a stimulation of the penicillinase. If he'd 



-1600 



200 I 



800 a 



-400 



60 120 180 240 300 350 

 ml 



Fig. 12. 



The fractionation of calf lens cortex fiber cell proteins. 

 The experimental conditions are the same as those 

 described for Fig. 10. (Fig. 10, J. Papaconstantlnou, 

 Science, in press; copyright 1966 by the American 

 Association for the Advancement of Science.) 



gotten no effect I could accept that argument; 

 but he got an effect. 



GROSS: He might have had the penicillinase 

 messenger still coming out, but the outflow of 

 others seriously depressed; so that you're 

 synthesizing the proteins from templates that 

 remain at a selectively higher rate. 



PAPACONSTANTINOU : Right, What you' re 

 essentially saying is that the penicillinase 

 region may not have as high a GC content as 

 some of the other regions. 



59 



