Mutations in the mitochondrial split gene COXI are preferentially located in exons: a mapping study of 170 mutants

Abstract

We have analysed the precise location of a large number (170) of mutations affecting the structural gene for subunit I of the cytochrome c oxidase complex. This gene, COXI, is 12.9 kb long and the major part of the sequence (i.e. 11.3 kb) is composed of introns. Several conclusions can be drawn from this study: (1) A significant proportion (84/170) of the mutations cannot be assigned to a single position within the gene by deletion mapping, in spite of clearly being located in it. These mutations are probably large deletions or multiple mutations. (2) Four mutants carry distant double mutations, which have been individually localized. (3) Eighty-two mutants have lesions that are restricted to very short regions of the gene and we therefore conclude that they are most probably due to single hits; amongst these single mutations, 41 are unambiguously located in exons and 28 in introns. This result implies that, at least in this particular split gene, the probability of selection of a mutant phenotype in an exon is, on the average, 13.3 times greater than in an intron, in spite of the existence, within most of these introns, of open reading frames specifying intronic proteins. The evolutionary significance and biological implications of these results are discussed.

The Saccharomyces cerevisiae OXA1 gene is required for the correct assembly of cytochrome c oxidase and oligomycin‐sensitive ATP synthase

“…They are both isonuclear to CW04. CG481 is isomitochondrial to 777-3A/G481 [5] and CV45 is isomitochondrial to ABI.4D/V45 [6]. NBT3 (alpha, ade2.1 oxal::URA3 his3-11,15 trpl-I leu2-3,112, rho + mit+[2i]) and NBT4 (alpha, ade2-1 oxal: :URA3 his3.11,15 trpl.1 ieu2-3o!12, rho + mit+[Ai]) carry the oxal ::URA3 deleted allele (see contruction below).…”

“…In order to analyse the consequence of these cytochrome defects on the oxidative phosphorylation activities, we have measured the succinate-cytochrome c reductase, cytochrome c oxidase and oligomycin-sensitive ATPase activities in the oxal Fig, 2 shows that in both oxal:: URA3 mutants, the cytochrome c oxidase activity is abolished, the succinatc-cytochrome c reductase activity is diminished and the oligomycin,sensitive ATPase activity is dramatically deceased, A priori, the diminution of cytochrome b and complex Ill activity as well as the strong decrease of ATPase activity could be either the direot effect of the lack of Oxalp or the consequence of the total absence of cytochrome aaa and cytochrome c oxidase activity, In order to see if a cytochrome oxidase deficient mutant would lead to such pleiotropic defects, we have constructed two other cytochrome c oxidase deficient strains isonuclear to NBT3 and NBT4 (see section 2), The strain CG481 carries the mutation coxl-G481 in the mitochondrial gene encoding the subunit I (COXI) of cyto-chrome oxidase [5]. The strain CV45 carries the mutation cox2-V45 in the mitochondrial gene encoding the subunit II (COXII) of cytochrome oxidase [6].…”

Molecular and biochemical analysis of Saccharomyces cerevisiae cox1 mutants

“…The mutations had been previously localized by deletion mapping in the mitochondrial COX1 gene (Netter et al 1982(Netter et al , 1995. Sequencing revealed that the mutations are in positions consistent with their location determined by deletion mapping.…”

“…All the strains are listed in Table 1. The mitmutants were isolated from the haploid strain 777-3A (op1), mapped to the COX1, COX2 or COX3 genes (Kotylak and Slonimski 1977) and were localized more precisely, for the cox1 mutants, by deletion mapping (Netter et al 1982(Netter et al , 1995. The cox2 mutant (V44) and the cox3 mutant (V206) have been previously described as defective in the synthesis of Cox2p and Cox3p respectively (Kruszewska et al 1980;Baranowska et al 1983).…”

Suppressors of cis -acting splicing-deficient mutations that affect the ribozyme core of a group II intron 1 1Edited by M. Yaniv

“…The position and size of the mtDNAs of the three rho À DNAs used as molecular probes are indicated in the upper part of the Figure. M21 and MA81 are probes for introns aI1 and aI2, respectively, while D8 corresponds to exon A4. The extremities of the D8 mtDNA have been determined by sequencing (Netter et al, 1995). Slanted edges symbolize remaining uncertainties as to the exact limits of the repetitive units of the M21 and MA81 mtDNAs (Carignani et al, 1986).…”