GENETIC CONTROL OF ENZYME STRUCTURE 7 



into two separate proteins, termed A and B (Crawford and Yanofsky, 

 1958). The coli A-protein has a molecnlar weight of about 29,500, 

 while that of the B-protein is not yet known. Physical contact be- 

 tween the A- and B-proteins appears to be required for significant 

 activity in any of the three reactions, although each protein alone 

 has slight activity in one of the reactions (A in reaction 2; B in reac- 

 tion 3) (Yanofsky, 1960). 



Reaction Catalyzed by 



Bgal PO4 



1. Indole glycerol phosphate + L-serine > L-tryptophan + triose phosphate 



Wild-type Tsase and some CRM's 



2. Indole glycerol phosphate ^=i indole -|- triose phosphate 



Wild-type Tsase and some CRM's 

 Bp.al PO_, 



3. Indole + L-serine > tryptophan 



Wild-type Tsase and some CRM's 



Fig. 1-1. The reactions catalyzed by wild-type tryptophan synthetase and 

 by certain CRM-proteins in N. crassa and £. coli. 



In both Neurospora and coli, many tryptophan-requiring mutants 

 have been isolated w^iich are defective in their ability to form normal 

 Tsase (Yanofsky and Bonner, 1955a). Genetic analyses have shown 

 that these mutants are all damaged within a small genetic region. 

 In Neurospora this region is called the td locus, and in E. coli, the 

 A and B genetic regions ( Yanofsky, 1960 ) . 



Using rabbit neutralizing anti-enzyme, prepared against highly 

 purified preparations of wild-tvpe Neurospora or coli tryptophan syn- 

 thetase, it is possible to scan extracts of the tryptophan-requiring 

 mutants for the presence of defective proteins which still retain 

 sufficient structural similarity to the normal enzyme to render them 

 serologically cross-reactive (Suskind et al., 1955; Suskind, 1957a; 

 Lerner and Yanofsky, 1957). 



In Neurospora and coli, many mutants are found which contain 

 cross-reacting material, called "CRM," although a number of mu- 

 tants do not (Suskind, 1957a; Lerner and Yanofsky, 1957). This 

 latter class are termed "CRM-less mutants." Thus, the Tsase mu- 

 tants can be divided into two different groups simply on the basis 

 of their ability to form CRM. 



Several obvious and important questions arise relating to the 

 finding of CRM's. ( 1 ) Are the CRM's mutationally altered proteins? 

 (2) Are the CRM's identical or do they represent a constellation of 



