12 CONTROL MECHANISMS IN CELLULAR PROCESSES 



larly when more information is available about the detailed struc- 

 ture of the CRM proteins and the normal proteins in both organisms. 



Studies on the structure of Tsase at the amino acid level are in 

 progress at Stanford, using the coli A-protein in order to compare 

 the peptide composition of normal A and of different A-CRM's. 



The A-protein is a highly purified crystalline protein (Hennmg, 

 1960) which behaves as a single component in the ultracentrifuge 

 and on electrophoresis. From the specific activity of the pure mate- 

 rial, it can be estimated that the amount of A-protein formed in 

 mutants grown on low levels of indole or tryptophan is of the order 

 of 1-2 per cent of the total extractable protein of the organism 



TABLE 1-1 



A Comparison of the Enzymatic Properties of the CRM Proteins in N. crassa 



and £. coli 



(Yanofsky, 1960). As mentioned earlier, many A-CRM mutants 

 have been isolated, and in view of the ease of isolation of the A-pro- 

 tein and its small size, it has received considerable attention using 

 chromatographic and electrophoretic separation methods (the "fin- 

 gerprinting" technique of Ingram, 1958 ) and also quantitative amino 

 acid analysis. 



A number of A-CRM's and the normal A-protein are being com- 

 pared in this manner. Preliminary results obtained by Dr. Helin- 

 ski at Stanford indicate that single peptide differences do exist 

 between the normal and three mutationally altered A-proteins ( He- 

 linski and Yanofsky). One can hopefully look forward to informa- 

 tion correlating changes in the primary structure of the A-protein 

 with specific genetically damaged sites within the Tsase region. 



Studies at the amino acid level with Neurospora Tsase have been 

 hampered by the difficulty of obtaining pure enzyme. Through the 

 work of Drs. Mohler and Carsiotis and Mrs. Ligon, the Neurospora 

 enzyme can now be routinely purified to a very high degree, and a 

 number of the physical properties of the purified protein have been 



