The molecular nature of mutations in the mt A-1 gene of the Neurospora crassa A idiomorph and their relation to mating-type function.
The 293-amino acid mt A-1 ORF of the A mating-type idiomorph of Neurospora crassa is multifunctional. It confers A mating identity and is responsible for heterokaryon incompatibility. The goal of this study was to dissect the functional regions of mt A-1. New mutants of mt A-1 selected for loss of the incompatibility function were obtained. One new mutant, A(m)99, was partially fertile as a maternal parent. This is the first time that fertility and incompatibility functions have been separated for the A idiomorph. In this mutant, the mt A-1 ORF is truncated after the first 85 amino acids, indicating that this N-terminal region is minimally sufficient for female fertility. A series of deletion constructs and frameshift alleles of mt A-1 was obtained and tested for male-mating activity and vegetative incompatibility in transformation experiments. These experiments showed that a region from position 1 to 111 is sufficient to confer incompatibility, while amino acids from position 1 to 227 are required for mating activity. A transcriptional analysis of mt A-1 showed that the mRNA is expressed both before and after fertilization. This, together with the phenotype of the A(m)99 mutant, suggests a post-fertilization function for mt A-1.
Saupe
S
S
Department of Botany, University of British Columbia, Vancouver, Canada.
Stenberg
L
L
Shiu
K T
KT
Griffiths
A J
AJ
Glass
N L
NL
D000483:Alleles; D000595:Amino Acid Sequence; D005656:Fungal Proteins / Q000235:genetics*; D017353:Gene Deletion; D005800:Genes, Fungal; D049770:Genes, Mating Type, Fungal; D008969:Molecular Sequence Data; D009154:Mutation; D009492:Neurospora crassa / Q000235:genetics*; D016366:Open Reading Frames; D014158:Transcription, Genetic; D014170:Transformation, Genetic
D005656:Fungal Proteins; C097997:MTA-1 protein, Neurospora crassa