GENETIC CONTROL OF ENZYME STRUCTURE 



n 



map, and a mutant retaining the In + Ser -^ Trypt reaction is at the 

 opposite end. It further appears that the CRM mutants having 

 Beal PO4 and Bcal PO^-serine requirements for the InGP ^ In + TP 

 reaction also fall into distinct genetic regions (Bonner et al., 1960). 

 These results are schematically summarized in Fig. 1-3, which 

 compares the genetic maps and tvpes of mutationally altered pro- 

 teins in coli and Neurospora. From the data already available, it 

 seems that there is a clustering; of mutationally altered sites which 



N. crassa 



B 



n + ser -^ Trypt 

 sites 



InGP^In+TP 

 sites 



E. coli 



Fig. 1-3. A schematic representation of the clustering of the genetic regions 

 (tc/ locus) which control the structure of tryptophan synthetase in N. crassa and 

 E. co//'. N. crassa: region 1, pyridoxal phosphate site; region 2, serine site. 



give rise to similar phenotypic aberrations (in terms of the type of 

 altered protein synthesized by the organism). Furthermore, there 

 appears to be a remarkable parallelism between the distribution of 

 mutationally altered sites causing similar effects in the two organ- 

 isms. The localization of Neurospora CRM formation into two major 

 genetic regions is comparable in effect to the localization of the coli 

 A and B genetic areas. In addition, as indicated in Table 1-1, the 

 enzymatic properties of the coli A- and B-CRM proteins can be com- 

 pared to the enzymatic properties of the different Neurospora CRM 

 proteins; thus, it seems that the organization of the genetic regions 

 controlling Tsase in coli and in Neurospora shows several striking 

 similarities. Further study should prove most informative particu- 



