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The linear mitochondrial DNAs of the two infertile algal species Chlamydomonas smithii and C. reinhardtii are co-linear with the exception of a 1 kb intron (alpha intron) located in the cytochrome b gene of C. smithii. C. smithii also possesses an additional HpaI restriction site (H marker) located in the COXI gene, about 5 kb from the intron. In reciprocal crosses, C. smithii (H+ alpha +) x C. reinhardtii (H- alpha -), the alpha intron is transmitted to all diploid progeny, whereas the H marker is frequently transmitted either biparentally or paternally depending on whether the C. smithii parent is maternal (mt+) or paternal (mt-). In diploids resulting from artificial fusion between vegetative cells, the absolute transmission of alpha is accompanied by the frequent transmission of the H+ marker, irrespective of the mating type of the parental strains. Finally, in reciprocal crosses between C. smithii (H+ alpha +) and recombinant H- alpha + clones, the transmission of the H marker is predominantly paternal or biparental. These results allow us to conclude that (1) the alpha intron behaves as a group I intron whose unidirectional conversion influences the transmission of the H marker; and (2) the mt- paternal mitochondrial genome is transmitted more often than the mt+. The mating type has no effect in diploids obtained by artificial fusion.
Mol Gen Genet 1990 Sep
PMID:Mitochondrial genome transmission in Chlamydomonas diploids obtained by sexual crosses and artificial fusions: role of the mating type and of a 1 kb intron. 225 Jun 46

The nuclear genome encoded yeast protein CBS2 is required for translational activation of mitochondrial cytochrome b RNA. Genetic studies have shown that the target sequence of the CBS2 protein is the 5' untranslated leader sequence of cytochrome b RNA. Here we report on the intracellular localization of CBS2. CBS2 protein, expressed in Escherichia coli and prepared from inclusion bodies, was used as an antigen to raise a polyclonal rabbit antiserum. Affinity-purified CBS2 antibodies detect a 45 kDa protein in mitochondrial lysates of wild-type cells, which is absent in a strain in which the CBS2 gene has been deleted. The protein is overexpressed in mitochondrial extracts of a transformant carrying the CBS2 gene on a high copy number plasmid, but undetectable in the post-mitochondrial supernatant. Intramitochondrial localization of CBS2 was verified by in vitro import of CBS2 protein that had been synthesized in a reticulocyte lysate programmed with CBS2 mRNA transcribed in vitro. Mitochondrial import of CBS2 is not accompanied by any detectable proteolytic processing.
Mol Gen Genet 1990 Sep
PMID:Identification of CBS2 as a mitochondrial protein in Saccharomyces cerevisiae. 227 79

RNA editing in the cytochrome b locus of Oenothera berteriana mitochondria modified a number of cytidine nucleotides to uridines, mostly altering codon identities. One nucleotide alteration involved a reverse modification changing a genomic thymidine to a cytidine in the cDNA sequence. The enzymatic editing activity in higher-plant mitochondria thus appears to be able to catalyze the interconversion of pyrimidines in both directions at specific nucleotides in the mRNA template.
Mol Cell Biol 1990 May
PMID:RNA editing in the cytochrome b locus of the higher plant Oenothera berteriana includes a U-to-C transition. 232 59

The 16,775 base-pair mitochondrial genome of the white Leghorn chicken has been cloned and sequenced. The avian genome encodes the same set of genes (13 proteins, 2 rRNAs and 22 tRNAs) as do other vertebrate mitochondrial DNAs and is organized in a very similar economical fashion. There are very few intergenic nucleotides and several instances of overlaps between protein or tRNA genes. The protein genes are highly similar to their mammalian and amphibian counterparts and are translated according to the same variant genetic code. Despite these highly conserved features, the chicken mitochondrial genome displays two distinctive characteristics. First, it exhibits a novel gene order, the contiguous tRNA(Glu) and ND6 genes are located immediately adjacent to the displacement loop region of the molecule, just ahead of the contiguous tRNA(Pro), tRNA(Thr) and cytochrome b genes, which border the displacement loop region in other vertebrate mitochondrial genomes. This unusual gene order is conserved among the galliform birds. Second, a light-strand replication origin, equivalent to the conserved sequence found between the tRNA(Cys) and tRNA(Asn) genes in all vertebrate mitochondrial genomes sequenced thus far, is absent in the chicken genome. These observations indicate that galliform mitochondrial genomes departed from their mammalian and amphibian counterparts during the course of evolution of vertebrate species. These unexpected characteristics represent useful markers for investigating phylogenetic relationships at a higher taxonomic level.
J Mol Biol 1990 Apr 20
PMID:Sequence and gene organization of the chicken mitochondrial genome. A novel gene order in higher vertebrates. 232 78

The fumarate reductase operon of Wolinella succinogenes is made up of three structural genes (frd-CAB). The frdC gene was located next to the promoter region and identified as the cytochrome b structural gene encoding 256 amino acid residues. The N-terminal amino acid sequences of seven fragments derived from the cytochrome b moiety of the enzyme all mapped within the frdC gene. This suggested that the enzyme contained only one species of cytochrome b. Re-evaluation of earlier measurements of subunit composition, haem B content and molecular weight led to the conclusion that the enzyme contained one molecule of cytochrome b with two haem B groups. The hydropathy plot of the amino acid sequence predicted five membrane-spanning hydrophobic segments, the first four of which contained a single histidine residue each. These residues could form the axial ligands to the two haem B groups. FrdC was found to be homologous with the cytochrome b (SdhC) of the Bacillus subtilis succinate dehydrogenase, but not with the hydrophobic subunits of the fumarate reductase or succinate dehydrogenase of Escherichia coli.
Mol Microbiol 1990 May
PMID:Wolinella succinogenes fumarate reductase contains a dihaem cytochrome b. 238 63

A full-length cDNA clone was isolated for the 47-kilodalton (kDa) subunit of the NADPH oxidase system, whose absence is responsible for the most common form of autosomally inherited chronic granulomatous disease (CGD). It encodes a 44.7-kDa polypeptide, which contains two src homology (SH3) domains and several possible sites for phosphorylation by protein kinase C. We speculate that the SH3 domains may interact with the Rap1 protein associated with cytochrome b-245 (M.T. Quinn, C.A. Parkes, L. Walker, S. Orkin, M. Dinauer, and A. Jesaitis, Nature [London] 342:198-200, 1989). An antiserum raised to the predicted C terminus of the protein detects a polypeptide with an apparent molecular mass of 47 kDa in normal neutrophil granulocytes but not in those from patients with autosomal CGD. The antibody has been used to show that the protein associates with the vacuolar membrane and is phosphorylated in response to phorbol ester treatment. Analysis of a number of tissue types and cell lines shows that expression of the gene is confined to phagocytic cells and B lymphocytes. This observation suggests that patients with CGD may also have a defect in lymphocyte function. p47 protein and mRNA levels increase during retinoic acid-induced neutrophil differentiation of HL60 cells. Nuclear run-on transcription assays show that the gene for p47 is induced at the transcriptional level in a cycloheximide-insensitive manner. These data indicate that this gene is a primary target for regulation by retinoic acid.
Mol Cell Biol 1990 Oct
PMID:Characterization of the 47-kilodalton autosomal chronic granulomatous disease protein: tissue-specific expression and transcriptional control by retinoic acid. 239 96

Epimastigote cultures of the two cloned Trypanosoma cruzi stocks, CA-I/72 and HO-3/15, grown under identical conditions, differ both qualitatively and quantitatively in their cytochrome content. The CA-I/72 stock has a four-fold higher cytochrome b content (19.2 nM (mg protein)-1) than the HO-3/15 stock (4.9 nM (mg protein)-1). Cytochrome o is present at 29 nM (mg protein)-1 in the CA-I/72 stock but is below detectable limits in the HO-3/15 stock. There is no inter-stock difference in oxygen utilization (12-15 nM O2 min-1 (mg protein)-1) during exponential growth. However, stationary phase CA-I/72 epimastigotes utilize twice as much oxygen as HO-3/15 epimastigotes. Oxygen utilization by HO-3/15 epimastigotes incubated in Dulbecco's phosphate buffer solution (starvation conditions), was stimulated earlier and to higher levels by the addition of glucose than by CA-I/72 epimastigotes under identical conditions. Under starvation conditions and with the cytochrome chain partially inhibited by antimycin A,(anti-A) the addition addition of glucose also increased oxygen utilization by CA-I/72 epimastigotes. In contrast, anti-A did not influence glucose-stimulated oxygen utilization by HO-3/15 epimastigotes. Following partial inhibition with anti-A, salicylhydroxamic acid produced an additional 50% inhibition in oxygen utilization in both stocks irrespective of the growth phase of the organisms. These data indicate that marked intra-specific differences in oxidative metabolism exist within the T. cruzi population and that an alpha-glycerophosphate oxidase or similar salicylhydroxamic acid-inhibitable compound may be present in the organism.
Mol Biochem Parasitol 1990 Feb
PMID:Isolate-dependent differences in the oxidative metabolism of Trypanosoma cruzi epimastigotes. 240 95

cyt18-1 (299-9) is a nuclear mutant of Neurospora crassa that has been shown to have a temperature-sensitive defect in splicing the mitochondrial large rRNA intron. In the present work, we investigate the effect of the cyt18-1 mutation on splicing of mitochondrial mRNA introns. Two genes were studied in detail; the cytochrome b (cob) gene, which contains two introns, and a "long form" of the cytochrome oxidase subunit I (coI) gene, which contains four introns. We found that splicing of both cob introns and splicing of at least two of the coI introns are strongly inhibited in the mutant, whereas splicing of coI intron 1, which is excised as a 2.6 X 10(3) base circle, is relatively unaffected. The rRNA intron and both cob introns are group I introns, whereas the circular coI intron may belong to another structural class. Control experiments showed that the degree of inhibition of splicing is greater in the mutant than can be accounted for by severe inhibition of mitochondrial protein synthesis. Finally, experiments in which mutant cells were shifted from 25 degrees C to 37 degrees C showed that splicing of the large rRNA precursor and splicing of the coI mRNA precursor are inhibited with similar kinetics. Considered together, our results suggest that the cyt18 gene encodes a trans-acting component that is required for the splicing of group I mitochondrial DNA introns or some subclass thereof. Since Neurospora cob intron 1 has been shown to be self-splicing in vitro, defective splicing of this intron in cyt18-1 indicates that an essentially RNA-catalyzed splicing reaction must be facilitated by a trans-acting factor, presumably a protein, in vivo.
J Mol Biol 1985 Aug 05
PMID:RNA splicing in Neurospora mitochondria. Defective splicing of mitochondrial mRNA precursors in the nuclear mutant cyt18-1. 241 16

The mitochondrial respiratory system is absent in slender bloodstream forms of Trypanosoma brucei, incomplete in stumpy bloodstream forms, and complete in procyclic (insect) forms. The steady-state abundance of transcripts of some mitochondrially encoded components of the respiratory system correlates with its differential expression in different life cycle stages. Recently, it was reported that uridines which are not encoded in the genome are added to cytochrome b and cytochrome oxidase II transcripts. We now report that the (U)+ transcripts of both genes are found in procyclic forms and to some degree in stumpy forms but are absent in slender forms. The uridine additions to cytochrome oxidase II correct a frameshift in the gene and presumably allow production of a full-length protein, whereas those added to cytochrome b create an in-frame AUG which extends the N terminus of the predicted protein by 20 amino acids. The stage specificity of uridine additions to these transcripts thus reflects the life cycle stage during which the protein products would be used. Transcripts of MURF2, a gene of unknown function, have additional uridines in both slender and procyclic forms which create two in-frame AUGs. MURF2 transcripts additionally differ from the DNA sequence in ways which cannot be explained by uridine addition alone, implying that other processes alter these transcripts.
Mol Cell Biol 1988 Mar
PMID:Developmental aspects of uridine addition within mitochondrial transcripts of Trypanosoma brucei. 245 74

The amino acid sequences of the protonmotive cytochrome b from seven representative and phylogenetically diverse species have been compared to identify protein regions or segments that are conserved during evolution. The sequences analyzed included both prokaryotic and eukaryotic examples as well as mitochondrial cytochrome b and chloroplast b6 proteins. The principal conclusion from these analyses is that there are five protein regions--each comprising about 20 amino acid residues--that are consistently conserved during evolution. These domains are evident despite the low density of invariant residues. The two most highly conserved regions, spanning approximately consensus residues 130-150 and 270-290, are located in extramembrane loops and are hypothesized to constitute part of the Qo reaction center. The intramembrane, hydrophobic protein regions containing the heme-ligating histidines are also conserved during evolution. It was found, however, that the conservation of the protein segments extramembrane to the histidine residues ligating the low potential b566 heme group showed a higher degree of sequence conservation. The location of these conserved regions suggests that these extramembrane segments are also involved in forming the Qo reaction center. A protein segment putatively constituting a portion of the Qi reaction center, located approximately in the region spanned by consensus residues 20-40, is conserved in species as divergent as mouse and Rhodobacter. This region of the protein shows substantially less sequence conservation in the chloroplast cytochrome b6. The catalytic role of these conserved regions is strongly supported by locations of residues that are altered in mutants resistant to inhibitors of cytochrome b electron transport.
J Mol Evol 1989 Aug
PMID:Evolutionary conservation of protein regions in the protonmotive cytochrome b and their possible roles in redox catalysis. 250 16


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