14 CONTROL MECHANISMS IN CELLULAR PROCESSES 



In several heterocaryons studied by Racbmeler and Yanofsky, 

 the tryptophan-independent heterocaryons were analyzed for the 

 type of Tsase using enzymatic and antigenic criteria. It appears 

 that these heterocaryons form several types of Tsase-like proteins. 

 They continue to synthesize the parental CRM type, they form 

 enzyme having normal properties, and there is some evidence for 

 a fourth Tsase-like protein. If this fourth protein type proves to be 

 a doubly defective molecule, it would suggest that recombination or 

 reconstitution of some type may also occur at the protein-forming 



td Gene ^71 2 16 6 3 7 24 1 



Mutational Sites 

 1,16 



2,71 



A 78 



3,24 



Complementation Map 



Fig. 1-4. A comparison of mutational site order and complementation maps 

 in N. crassa. When two lines in the complementation map overlap, these mutants 

 will not complement. Conversely, mutants which are not in overlapping groups 

 will complement. 



level. It should prove of great interest to determine the structure 

 of these heterocaryon proteins and also to assess the effects of rela- 

 tive nuclear input, P'^- decay, and other factors on the role of nuclear 

 and cytoplasmic elements in complementation. 



A second type of interaction can be found in the cases of partial 

 reversion in Neurospora and coli Tsase mutants ( Yanofsky and Craw- 

 ford, 1959; Esser et at., 1960). Reversion in a biochemical mutant 

 is thought to be due to a change at the same genetic site as the 

 original mutation, restoring the original genetic information or nu- 

 cleotide sequence in the wild-type gene. This change allows func- 

 tioning of the gene in a normal manner, and normal growth occurs 

 in the absence of a nutritional supplement. In some instances one 

 finds a second type of reversion in which the growth rate of the 

 revertant is slower than the original wild tvpe. These are called 

 'partial reversions." 



