CLONING AND ANALYSIS OF THE ALTERNATIVE OXIDASE GENE OF NEUROSPORA-CRASSA

Mitochondria of Neurospora crassa contain a cyanide-resistant alternat ive respiratory pathway in addition to the cytochrome pathway. The alt ernative oxidase is present only when electron flow through the cytoch rome chain is restricted. Both genomic and cDNA copies for the alterna tive oxidase gene have been isolated and analyzed. The sequence of the predicted protein is homologous to that of other species. The mRNA fo r the alternative oxidase is scarce in wild-type cultures grown under normal conditions, but it is abundant in cultures grown in the presenc e of chloramphenicol, an inhibitor of mitochondrial protein synthesis, or in mutants deficient in mitochondrial cytochromes. Thus, induction of alternative oxidase appears to be at the transcriptional level. Re striction fragment length polymorphism mapping of the isolated gene de monstrated that it is located in a position corresponding to the aod-1 locus. Sequence analysis of mutant aod-1 alleles reveals mutations af fecting the coding sequence of the alternative oxidase. The level of a od-1 mRNA in an aod-2 mutant strain that had been grown in the presenc e of chloramphenicol was reduced several fold relative to wild-type, s upporting the hypothesis that the product of aod-2 is required for opt imal expression of aod-1.