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Query: UNIPROT:P06889 (Mol)
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The complete nucleotide sequence of the circular mitochondrial (mt) DNA of the chlorophyte alga Prototheca wickerhamii has been determined (55,328 base-pairs, A+T content 74.2%). The genes identified encode three subunits of the cytochome oxidase, apocytochrome b, nine subunits of the NADH dehydrogenase complex (nad1 to 7, nad4L and nad9), three ATPase subunits (atp6, atp9, atp1 (also referred to as atpA)), three ribosomal RNAs (5 S (rrn5), small subunit (srn) and large subunit (lrn) RNA), 26 tRNAs, and 13 ribosomal proteins. A total of five group I introns reside in lrn and cox1, two of which include intronic open reading frames (ORFs). Five free-standing ORFs longer than 60 codons are present. Three of these ORFs are counterparts to genes encoding proteins of unknown function in plant mitochondria (orf25 and orfB of angiosperms and orf244 of liverwort), whereas two of them are unique. Mitochondrial genes are encoded on both DNA strands in a way that suggests the existence of two transcription units, each including approximately one half of the mitochondrial genome. The two intergenic regions in which transcription is believed to initiate and terminate are about ten times longer than the other intergenic regions (1118 and 1993 nt versus 100 to 150 nt). A total of 29 recurring sequence motifs (30 to 200 nt long) have been found in intergenic regions. Nine different types of motifs are present, most of them arranged as tandem repeats. These motifs may be implicated in transcription, e.g. as signals for initiation, termination and/or processing. Phylogenetic analysis on the basis of the cox1 gene strongly suggested that P. wickerhamii and plant mitochondrial genomes are monophyletic. The finding of plant-specific mitochondrial genes such as orf25, orf244, orfB and rrn5 in P. wickerhamii mitochondria corroborates this idea.
J Mol Biol 1994 Mar 18
PMID:Complete sequence of the mitochondrial DNA of the chlorophyte alga Prototheca wickerhamii. Gene content and genome organization. 813 22

The mitochondrial gene coding for subunit 4 of the NADH dehydrogenase complex I (nad4) has been isolated and characterized from lettuce, Lactuca sativa. Analysis of nad4 genes in a number of plants by Southern hybridization had previously suggested that the intron content varied between species. Characterization of the lettuce gene confirms this observation. Lettuce nad4 contains two exons and one group IIA intron, whereas previously sequenced nad4 genes from turnip and wheat contain three group IIA introns. Northern analysis identified a transcript of 1600 nucleotides, which represents the mature nad4 mRNA and a primary transcript of 3200 nucleotides. Sequence analysis of lettuce and turnip nad4 cDNAs was used to confirm the intron/exon border sequences and to examine RNA editing patterns. Editing is observed at the 5' and 3' ends of the lettuce transcript, but is absent from sequences that correspond to exons two, three and the 5' end of exon four in turnip and wheat. In contrast, turnip transcripts are highly edited in this region, suggesting that homologous recombination of an edited and spliced cDNA intermediate was involved in the loss of introns two and three from an ancestral lettuce nad4 gene.
Mol Gen Genet 1994 Apr
PMID:Intron loss from the NADH dehydrogenase subunit 4 gene of lettuce mitochondrial DNA: evidence for homologous recombination of a cDNA intermediate. 819 77

Mammalian heart mitochondria (MT) contain a potent Mg(2+)-dependent DNA endonuclease that becomes soluble once isolated mitochondria are disrupted using detergent. The level of this endonuclease was previously found to be markedly elevated in adult rat heart compared to other adult rat tissues. Among tissues, the level of the MT endonuclease does not appear to be correlated with the rate of MT DNA replication but rather with the rate of oxidative metabolism [Houmiel, K.L., Gerschenson, M. and Low, R.L., 1991. Biochimica Biophysica Acta 1079: 197-202]. In the present study, the level of the endonuclease has been quantitated both during rat cardiac development, from gestational day 18 through adulthood, and in cultured rat heart myoblasts. Surprisingly, the specific activity of the MT endonuclease in fetal and newborn mitochondria is high. The values are greater than 50% of that seen in the adult even though the mitochondria at this period of heart development are few and structurally disorganized. Remarkably, there is a burst of endonuclease activity at day 2 which accompanies a similar, transient elevation of respiratory complex I and IV activities. At later times, the endonuclease activity gradually increases until adulthood and correlates with steady increases in MT DNA and DNA polymerase-gamma. In cultured myoblasts, the level of the endonuclease increases about seven-fold as the growing cells reach confluency and differentiate into myotubes. These variations in the specific activity of the endonuclease, when considered along with other properties of the enzyme suggest that the endonuclease may serve a role in the removal of oxidative damage in MT DNA incurred from respiration.
J Mol Cell Cardiol 1994 Jan
PMID:Levels of the mitochondrial endonuclease during rat cardiac development implicate a role for the enzyme in repair of oxidative damage in mitochondrial DNA. 819 67

Genes homologous to those encoding mitochondrial NADH dehydrogenase subunits ND4L and ND5 in filamentous fungi were identified in the mitochondrial genome of a budding yeast, Hansenula wingei. The structure and expression of these genes were investigated. The H. wingei ND4L gene is 282 bp long, and potentially codes for a polypeptide of 94 amino acids. The putative ND4L protein sequence shares about 46% homology with the analogous mitochondrial proteins of filamentous fungi. The H. wingei ND5 gene is 1935 bp long, and encodes a 645-residue polypeptide. The derived ND5 protein shares about 38% sequence homology with the analogue in filamentous fungi. The ND4L and ND5 genes have no intervening sequence, and form a gene cluster in the order of 5'-ND4L-ND5-3'. A presumptive mature dicistronic or polycistronic transcript of these genes was detected by Northern blot hybridization. These results strongly indicate that these ND4L and ND5 genes are active. As far as we are aware, this is the first report on the identification of mitochondrially encoded ND genes in yeast.
Mol Gen Genet 1994 May 25
PMID:The mitochondrial genome of yeast Hansenula wingei encodes NADH dehydrogenase subunit genes ND4L and ND5. 820 91

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine is a potent mutagenic agent produced during thermal processing of meats. Since 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine has a similar structure to tetrahydroisoquinoline, a mitochondria toxic compound, we determined whether or not this compound shows detrimental effects on mitochondrial electron transport activities in various rat tissues. Administration of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, 100 mg/kg twice a week for 4 weeks, decreased significantly the activity of complex I in mitochondrial electron transport chain of heart, diaphragm, and psoas major, while it did not affect the activities of complex I in the liver mitochondria. Concerning the activities of complexes II, III, and IV, no significant effects were observed irrespective of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine administration. Age-related deterioration of mitochondrial function seems to be a major contributor to age-related decline in cellular function. From our results, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine might act as an accelerator of age-related decline in mitochondrial function.
Biochem Mol Biol Int 1993 Aug
PMID:Detrimental effects of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, a mutagenic agent, on mitochondrial respiration among various rat tissues. 822 Feb 32

We determined skeletal muscle, heart and liver mitochondrial electron transport activities in rats and dogs of various ages. In the skeletal muscle mitochondria, decrease in the activity of complex I was observed in rats aged 28 weeks, and further reduction of the activity was observed in rats aged 55 weeks. A significant decrease in complex IV activity was observed in rats aged 55 weeks. No significant reduction in complex II and III activities were observed in rats aged up to 100 weeks. Significant decreases in complex I and IV activities were observed in heart muscles of rats aged 100 weeks, while no significant changes in the activity of complex I in liver mitochondria were observed in rats aged up to 100 weeks. Similar results were obtained in dogs, i.e., the activity of complex I was the most susceptible to aging among the activities of complexes; and skeletal muscle mitochondria were the most susceptible to aging among the tissues. From our results, involvement of mitochondria in the development of age-related decline in cellular function is especially emphasized in post mitotic cells, and age-associated mitochondrial functional changes are stressed in mitochondrial complexes which contain mitochondrial DNA-encoded subunits.
Biochem Mol Biol Int 1993 Aug
PMID:Changes in skeletal muscle, heart and liver mitochondrial electron transport activities in rats and dogs of various ages. 822 Feb 42

From a sugar beet mitochondrial DNA library, we have isolated an open reading frame (ORF192) showing extensive homology to the gene for the 30 kDa subunit of the bovine mitochondrial complex I (NADH: ubiquinone reductase). The ORF192 was found to be actively transcribed to give an RNA of approximately 1.0 kb. We have designated this gene nad9. Transcripts from the nad9 locus are edited by five C to U transitions, increasing similarity with the amino acid sequence of the corresponding bovine and Neurospora crassa polypeptides. Southern blot hybridization also indicates that nad9 is present in the mitochondrial genomes of a variety of higher plant species.
Mol Gen Genet 1993 Nov
PMID:The sugar beet mitochondrial genome contains an ORF sharing sequence homology with the gene for the 30 kDa subunit of bovine mitochondrial complex I. 824 3

Transposition of Tn5 requires the binding of the transposase protein to the transposon outside end (OE) DNA sequences. Transposase mutants that increase the transposition frequency result in the formation of two distinct transposase/OE DNA complexes, observed by gel retardation analysis. The slower migrating complex I, also formed by wild-type transposase, contains protein oligomers of transposase and transposase related proteins. The faster migrating, novel complex II is caused by the binding of monomeric, proteolytic transposase fragments gamma and delta that have lost the carboxy-terminus of the protein. Transposase gamma and delta bind OE DNA with a high apparent affinity but are unable to promote transposition in vivo. We propose that the transposase protein is functionally unstable and can undergo a conformational change that reduces the activity but protects the protein from proteolysis. The transposase mutants favor the more active but proteolytically hypersensitive protein conformation.
J Mol Biol 1994 Jan 14
PMID:Interaction of Tn5 transposase with the transposon termini. 828 77

The M(r) 30,000 polypeptide of the hydrophobic protein fraction of the energy-transducing NADH-ubiquinone oxidoreductase (complex I) of bovine heart mitochondria was identified as the ND2 gene product based on a comparison of amino acid analysis and partial N-terminal sequencing results with the known DNA sequence of ND2 (Anderson, S. et al. (1982) J. Mol. Biol. 156, 683-717). A simple purification procedure was devised for this ND2 gene product. The procedure, which is described, involves treatment of bovine complex I with a chloroform-methanol (2:1 [v/v]) solution. The antiserum raised against this purified bovine ND2 gene product cross-reacted with the approximately M(r) 39,000 polypeptide extracted from the Paracoccus denitrificans membranes with chloroform-methanol (2:1 [v/v]).
Biochem Mol Biol Int 1993 Jun
PMID:Isolation and characterization of the ND2 polypeptide of the bovine energy-transducing NADH-ubiquinone oxidoreductase (complex I). 836 7

The subcutaneous administration of methyl isocyanate (MIC) in 1.0 LD50 dose in rats caused a significant effect on hepatic mitochondrial function only at complex I region of the respiratory chain. MIC administration at 1.0 LD50 dose also resulted in significant increases in malondialdehyde and ferrous ion concentration in liver mitochondria. It is suggested that the augmented lipid peroxidation in hepatic mitochondria, catalyzed by iron, possibly mobilized from intracellular stores leads to the inhibition of enzymes of mitochondrial respiration at complex I region, in vivo, in rats receiving a lethal dose of MIC subcutaneously.
Biochem Mol Biol Int 1993 Jul
PMID:Role of lipid peroxidation in impairment of mitochondrial function at complex I by methyl isocyanate treatment of rats in vivo. 840 Dec 98


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