X-ray-induced specific-locus mutations in the ad-3 region of two-component heterokaryons of Neurospora crassa. VII. Genetic lesions resulting in gene/point mutations at the ad-3B locus have different dose-response relationships.

Genetic characterization of X-ray-induced ad-3 mutants, induced in a two-component heterokaryon (H-12) of Neurospora crassa, has been performed to determine genotype, patterns of allelic complementation, and leakiness, and to distinguish gene/point mutations from multilocus deletions and multiple locus mutations (de Serres, 1989c, 1990a). The array of genotypes in the classes and subclasses in the spectrum of ad-3 mutants induced by a mutagenic agent constitute its mutagenicity profile; for X-rays this profile consists of 29 different genotypes. In the present paper, the data on gene/point mutations induced at the ad-3B locus (designated ad-3BR mutations) have been tabulated as a function of X-ray dose to determine the dose-dependent relationships of complementing and noncomplementing mutants. This analysis has shown that the overall percentages of mutants showing allelic complementation and the percentages of complementing mutants with nonpolarized patterns (both leaky and nonleaky) and noncomplementing mutants were dose-dependent; the former class decreased with increasing X-ray dose, and the latter class increased with increasing X-ray dose. The percentages of complementing mutants with polarized patterns were X-ray dose-independent. In addition, an unexpectedly high frequency of mutants with nonpolarized complementation patterns are discontinuous and probably result from multiple-site mutations.