GENETIC CONTROL OF ENZYME STRUCTURE 13 



studied (Moliler and Suskind, 1960; Carsiotis et al., 1960). Fine 

 structure studies on the normal and mutant Neurospora proteins 

 should be possible in the near future. Recently, Neurospora Tsase 

 has been subjected to trypsin digestion in tlie hopes of differentially 

 inactivating the enzymatic and antigenic activities of the molecule. 

 It was found that wild-type Tsase enzymatic actiyity can be de- 

 stroyed rapidh' by trypsin, while antigenic actiyity disappears only 

 after prolonged incubation (Garrick and Suskind, 1960). Hence it 

 is possible to obtain preparations with no enzymatic but consider- 

 able antigenic activity. The effect of trypsin on the activity of sev- 

 eral CRM's is being examined, and the use of other proteolytic 

 enzymes is anticipated. Since mutations at the td locus are able 

 to cause the loss of all or only part of the enzymatic activity of Tsase, 

 it is tempting to hope that analysis of the trypsin-prepared frag- 

 ments and the antigenically active residue may provide a clue as 

 to those amino acids essential for enzymatic and antigenic activity. 

 Perhaps this approach wall also offer a more systematic means for 

 analyzing CRM-less mutants at the structural level. 



For some time it has been known that certain allelic strains of 

 Neurospora, which are defective for a particular enzymatic activity, 

 can regain this activity when they are in a heterocaryon— that is, a 

 mycelium containing nuclei of unlike types. This phenomenon, 

 called "intragenic complementation," has been employed in the 

 Neurospora Tsase system to determine to what extent mutants which 

 show different CRM properties will cooperate to form a functional 

 Tsase. Studies at Yale (Lacy and Bonner, 1958; Lacy, 1959) and 

 at Stanford (Raclimeler, 1960) have provided some information on 

 this problem. They have found that tryptophan independent hetero- 

 caryons can be formed between four to live groups of td mutants. 

 Fig. 1-4 shows the relative order of mutational sites in the td locus 

 of Neurospora determined by recombination analysis, as well as a 

 complementation map prepared on the basis of heterocaryon tests. 



Several observations concerning the CRM proteins are available 

 from these complementation studies (Bonner et al., 1960). CRM 

 formation is required for complementation, and in several instances 

 the CRM's produced bv the contributing mutants are structurally 

 and functionally different. The fact that effective complementation 

 requires CRM formation by both participating mutants suggests the 

 existence of repair mechanisms involving specific protein— protein 

 interactions (Woodward, 1960). 



