Cytochrome oxidase subunits

Kornblatt, J.A., and Lake, D.F. (1980) Cross-linking of cytochrome oxidase subunits with difluorodini-trobenzene. Can. J. Biochem. 58, 219-224. 

Some mRNAs are edited before translation. The initial transcripts of the genes that encode cytochrome oxidase subunit II in some protist mitochondria do not correspond precisely to the sequence needed at the... 

FIGURE 2 RNA editing of the transcript of the cytochrome oxidase subunit II gene from Trypanosoma brucei mitochondria, (a) Insertion of four U residues (pink) produces a revised reading frame, (b) A special class of guide RNAs, complementary to the edited product, may act as templates for the editing process. 

The cytochrome oxidase subunit I (COI) gene of the mitochondrial genome has been isolated and sequenced from C. salaris and C. thy-malli (Meinila et al., 2002 Hansen et al., 2003). The COI gene was proven to be polymorphic and different haplotypes were found in both species. Monophyletic origins of the COI variants for C. salaris and C. thymalli were not confirmed. This gene has also been used to study the population genetics of C. salaris (see section on Molecular Analysis within Monogenean Species ). 

Several additional lines of evidence indicate that presequence function is governed by conformational properties of the precursor. The target peptide of yeast mitochondrial cytochrome oxidase subunit IV (COX), fused to murine dihydrofolate reductase (DHFR, a cytoplasmic enzyme). 

Peek, A.S., Gustafson, R.G., Lutz, R.A. and Vrijenhoek, R.C. (1997) Evolutionary relationships of deep-sea hydrothermal vent and cold-water seep clams (Bivalvia Vesicomyidae) results from the mitochondrial cytochrome oxidase subunit. Marine Biology, 130, 151. 

Map of the human mitochondrial genome. ND refers to NADH dehydrogenase subunits, CO denotes cytochrome oxidase subunits, and cytochrome B is shown as cyt b. The D-loop is required for mitochondrial genome replication. Most of the genes are encoded by the H-strand (outer circle). Locations of several LHON mutations known are shown by an "X."... 

FIG. 1.4 An example of kinetoplastid pan-editing. A portion of the mature T. brucei cytochrome oxidase subunit III is shown above a guide RNA. Uridines inserted via editing are shown in lower case. Insertion of the uridines within the box is directed by a different guide RNA not shown. For details see text and ref. (45). 

A similar inconsistency exists concerning oxidative phosphorylation in AD. Although activities of enzymes of the mitochondrial electron transfer chain are reported to be normal in AD brain, partial uncoupling of oxidative phosphorylation (electron transfer and phosphorylation of adenosine diphosphate are normally functionally linked) (Sims et al., 1987) and overexpression of cytochrome oxidase subunit-3 gene in cerebral temporal cortices (Alberts et al., 1992) have been reported. In addition, substantial decreases of complex IV activity were detected in platelets from five patients with AD (Parker et al., 1990). 

Sturm NR, Simpson L. Kinetoplast DNA minicircles encode guide RNAs for editing of cytochrome oxidase subunit III mRNA Cell 1990 61(5) 879-84. 

Hong WK, Han EH, Kim DG et al. (2007) Amyloid-beta-peptide reduces the expression level of mitochondrial cytochrome oxidase subunits. Neurochem Res 32, 1483-1488. 

Two types of mRNA editing are insertional and substitutional editing. Inser-tional editing includes (a) insertion or deletion of one or more U residues [typically in mitochondrial mRNAs such as cytochrome oxidase subunits II (coxll) and III of trypanosomatids (130—132)], (b) insertion of nontemplated C residues [e.g., single C insertion at 54 sites within 528 codons of mitochondrial mRNA for ATP synthetase a subunit of a slime mold, Physarum polycephalum (133)], and (c) insertion of one or more nontemplated G s [in paramyxovirus P mRNAs (134— 136)]. In substitutional editing, templated C is replaced by U (or vice versa) in the mitochondrial mRNAs [e.g., cytochrome c oxidase subunit 2 (cox2) of plants (137-139), chloroplast mRNA (140), and apolipoprotein B mRNA of mammalian cells (141,142). 

Which of these cytochrome oxidase subunits are associated with heme is, however, not yet known with certainty. The little information available is still contradictory. ... 

In order to define the translation site of the individual cytochrome oxidase subunits, cytochrome oxidase was purified from double-labeled cells. These had first been labeled with [ C]leucine in the absence of inhibitors, followed by labeling with [ H]leucine, either in the absence of inhibitors or in the presence of cycloheximide or chloramphenicol (see Section 2). The purified cytochrome oxidase was subsequently separated into subunits by gel electrophoresis in dodecylsulfate. The distribution of and H radioactivity was analyzed (Table I, Fig. 7). 

In untreated cells serving as control (labeling procedure 1, Section 2) no significant difference in the H/ C ratio of the seven cytochrome oxidase subunits could be detected (Fig. 7A). This indicates that these subunits... 

From labeling experiments II and IV (Table I, Figs. 7B and D), the following conclusion can be drawn The three large cytochrome oxidase subunits are mitochondrial translation products their labeling is insensitive to cycloheximide, but is sensitive to chloramphenicol. The four small cytochrome oxidase subunits are cytoplasmic translation products their labeling is sensitive to cycloheximide, but is insensitive to chloramphenicol. 

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