COMPARATIVE COMPLEMENTATION AND GENETIC MAPS OF THE PAN-2 LOCUS IN NEUROSPORA CRASSA

Abstract

The present study has utilized 75 mutants at the pan-2 locus in Neurospora craasa. This locus controls the conversion, in the biosynthesis of pantothenic acid, of keto-valine to keto-pantoic acid, a reaction presumably catalyzed by a single enzyme in this organism. All 75 mutants were tested in all possible pair-wise combinations for their ability to complement in heterocaryons. Twenty-three of the mutants gave at least one positive response, the remaining 52 failing to complement in any combination. The 23 complementing mutants comprise 12 different groups (types) and these 12 types can be arranged in a linear (one-dimensional) sequence to form a complementation map of the pan-2 locus. The relationships of mutants on this complementation map have been compared with their relationships on a genetic map of the locus derived from analysis of recombination. Although there is, in general, a rather marked agreement in the ordering of mutants on the two maps, certain marked exceptions to complete "co-linearity" occur. Various possible interpretations of interallelic complementation and of the relationship of this phenomenon to genetic fine structure are discussed. Particular consideration is given to the characteristics of interallelic complementation as they relate to the problem of defining a genetic unit of function.