16 



CONTROL MECHANISMS IN CELLULAR PROCESSES 



suppression (Suskind et ah, 1955). None of the CRM-less mutants 

 are affected by any of the known suppressor genes. However, the 

 CRM requirement is a necessary but not sufficient one for suppres- 

 sion, since there is at least one CRM mutant which is also non-sup- 

 pressible. The coli CRM-less mutants, on the other hand, do re- 



Fig. 1-5. The specificity of suppressor genes afFecting mutational sites within 

 the td locus of N. crassa. A plus sign indicates suppression. (Data adapted 

 from Yanofsky and Bonner, 1955a.) 



spond to suppressor genes (Yanofsky and Crawford, 1959). This 

 difference may be related to the sensitivity of the methods for de- 

 tecting CRM proteins. Whatever the explanation, the CRM re- 

 quirement for suppression in Neurospora suggests that protein of a 

 certain type or limiting size must be made or that the system for 

 synthesizing the protein must be available before suppressor gene 

 action can be effectively exerted. 



In all of the suppressed Tsase mutants of Neurospora and coli, one 

 characteristically finds very low levels of functional Tsase as com- 

 pared to the wild-type enzyme level ( Yanofsky and Bonner, 1955a ) . 



