MECHANISMS OF GENE ACTION 



293 



FIGURE 10.10. The ad, lo- 

 cus of Neurospora. Comple- 

 mentation map of the adf 

 locus based on both primary 

 and secondary mutants. Ro- 

 man numerals denote seven 

 distinct functional regions. The 

 figure above each line denotes 

 the number of independent 

 od4 mutants in each category 

 (from Giles, 1959, Proc. X 

 Infer. Congr. Genetics, Mon- 

 treal, 1958, 1:261). 



exists for this locus, as shown in Figure 10.10, but only a poor genetic 

 map is available owing to the infertility of crosses. Those mutant strains 

 which have been mapped indicate the same correlation between comple- 

 mentation map and genetic map seen at the pan-2 locus. Because of 

 the availability of an enzyme assay method, the extent of restoration of 

 activity by various pairs of mutants could be determined. As indicated 

 in Figure 10.11, a correlation was observed between enzyme activity, 

 and the map distance between members of complementing pairs of mu- 

 tants. In this material, more distant alleles complement more effectively 

 than do close ones. 



012345678 



Map Distance (Number of Complementation 

 Units Separating Mutants) 



FIGURE 10.11. Complementation and enzyme activity at the od4 locus. Relationship 

 between complementation map distance and odenylosuccinase activity in heterokaryons. 

 Each point represents a heterokaryon composed of diflPerent pairwise combinations of 

 adenylosuccinaseless mutants. Many of these figures are averages from several assays 

 of separately grown cultures of the heterokaryons. The data show a definite rela- 

 tionship in which the enzyme activity of the heterokaryons increases with increasing 

 map distance between the complementing alleles (after Woodward, 1959, Proc. Nafl. 

 Acad. Sci. Wash., 45:846). 



