ISSN:
1432-0983
Keywords:
Neurospora
;
Cytochrome c oxidase
;
COXII
;
Mitochondria
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary The maternally inherited [exn-5] mutant of Neurospora crassa is characterized by its slow-growth rate and deficiency of cytochrome aa 3 relative to wildtype strains. We have determined the DNA sequence of the COXI and COXII genes of the mutant, which encode subunits 1 and 2 of cytochrome c oxidase, respectively. No changes in the DNA sequence of the COXI gene relative to the corresponding wild-type gene were found. In the region of the COXII gene we found two alterations, one a C to T transition eight base pairs upstream of the coding sequence and the second within the coding sequence for subunit 2 affecting amino acid 27 of the precursor polypeptide (amino acid 15 of the mature polypeptide). The altered codon in [exn-5] specifies an isoleucine residue rather than the wild-type threonine residue. The corresponding position in subunit 2 sequences of all other organisms examined is conserved either as a threonine or a serine residue. Thus, we consider it likely that the mutation directly affecting the coding sequence of the polypeptide is responsible for the [exn-5] phenotype. Analysis of serially passaged heterokaryons constructed between wild-type and [exn-5] shows that both mutations segregate with the [exn-5] phenotype. Examination of mitochondrial translation products in [exn-5] revealed a deficiency of subunit 2, as well as the presence of a polypeptide that corresponds to a previously described precursor of subunit 1 that accumulates in a COXI mutant of N. crassa, [mi-3]. We propose possible relationships between [exn-5], [mi-3], and the nuclear su-1 [mi-3] allele, which suppresses both mutations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00312774
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