Mitochondrial rRNA

Mitochondrial rRNA labeled in vivo exclusively hybridizes to the H strand of mt DNA. Saturation hybridization experiments indicated that the large rRNA hybridizes with about 4 of the DNA, the small mt rRNA saturated at 2-3, and the 4 S RNA at 3.5%, a total of about 10% of the DNA, or about 20% of the sequences on one mt DNA strand. No cross reaction was found between microsomal rRNA from Xenopus and mt DNA. Dawid (1972) also stated that other uncharacterized mito-... 

Since it appears by now well established that the mitochondrial rRNAs, and at least the bulk of its tRNAs, are distinct from the species found in the cytosol, both in their nature and in their mode of specification by being mitochondrial transcripts (for reviews see introduction), we have recently concentrated our attention on mitochondrial mRNA. This species is, of course, of the greatest interest, not only because of its intrinsic importance to problems of mitochondrial autonomy, but also because the possibility of its nuclear origin and import into the mitochondria has been explicitly raised by several investigators. We have tried to obtain an answer to this question by means of the following paradigm. Three possible models can be envisaged ... 

The lack of assembly of a functional system in the mitochondria of cytoplasmic petite mutants is a complex question. It may be stated that many p" petites do not contain either of the mt rRNA cistrons, while, obviously, p petites must contain neither. However, some p" petites do contain one or the other, and, rarely, some petites contain parts of both cistrons, but whether they are entire is still an unsolved question. It is also questionable whether the simple presence of mtRNA is sufficient for assembly of a complete ribosomal system in a petite that may contain both mitochondrial rRNA cistrons in their entirety. It may be that the components of the mitochondrial membrane with which the system becomes associated are different than those in chloramphenicol-treated cells or that the permeability properties of the petite mitochondrial membrane are so changed that the cytoplasmically synthesized components cannot pass into the interstices of the organelle. However, even if functional ribosomes are assembled correctly, mitochondrial tRNAs may not be available if their genes are deleted. 

In order to examine this possibility, the rRNAs from bound 80 S and free cytoplasmic ribosomes were purified and examined by SDS polyacrylamide gel electrophoresis. Under the conditions of electrophoresis (conditions sufficient to completely resolve HeLa, E. coli, yeast cytoplasmic, and intrinsic mitochondrial rRNA), bound and free rRNA coelec-trophorese. This result demonstrates that there is no gross size difference between bound and free rRNA. Both ribosomes contain equal quantities of 5.8 S rRNA, which also coelectrophorese. 

Mitochondria are unique organelles in man and higher animals in that they contain their own genome. Mitochondrial DNA (mtDNA) in humans is a small (16.5 kb), circular genome that encodes only 13 proteins, 22 transfer RNA (tRNA), and 2 ribosomal RNA (rRNA) molecules. mtDNA is inherited only from the mother and is present in multiple copies within one mitochondrion. 

Mitochondrial DNA is transcribed as a polycistronic RNA which is subsequently cleaved to generate the various mature mRNA, tRNA, and rRNA (Clayton, 1984). The 13 proteins encoded by mtDNA are all components of the respiratory chain and are seven subunits of complex I, one subunit of complex III, three subunits of complex IV, and two subunits of complex V. 

Mitochondria are unique organelles in that they contain their own DNA (mtDNA), which, in addition to ribosomal RN A (rRNA) and transfer RN A (tRNA)-coding sequences, also encodes 13 polypeptides which are components of complexes I, III, IV, and V (Anderson et al., 1981). This fact has important implications for both the genetics and the etiology of the respiratory chain disorders. Since mtDNA is maternally-inherited, a defect of a respiratory complex due to a mtDNA deletion would be expected to show a pattern of maternal transmission. However the situation is complicated by the fact that the majority of the polypeptide subunits of complexes I, III, IV, and V, and all subunits of complex II, are encoded by nuclear DNA. A defect in a nuclear-coded subunit of one of the respiratory complexes would be expected to show classic Mendelian inheritance. A further complication exists in that it is now established that some respiratory chain disorders result from defects of communication between nuclear and mitochondrial genomes (Zeviani et al., 1989). Since many mitochondrial proteins are synthesized in the cytosol and require a sophisticated system of posttranslational processing for transport and assembly, it is apparent that a diversity of genetic errors is to be expected. 

Shrimp Primer for shrimp detechon, FASMAC Co., Ltd. 16S rRNA gene of mitochondrial DNA 187... 

Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. The remaining genes provide instructions for making molecules called transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which are chemical cousins of... 

The circular mitochondrial chromosome encodes 13 of the more than 80 proteins that comprise the major complexes of oxidative phosphorylation as well as 22 tRNAs and 2 rRNAs. Mutations in these genes affect highly aerobic tissues (nerves, muscle), and the diseases exhibit characteristic mitochondrial pedigrees (maternal inheritance). 

All eukaryotic cells in our bodies contain the same 23 chromosomes with the same DNA base sequences. The lone differences are the mitochondria. The mitochondria in typical somatic cells contain less than 0.1% of the cell s DNA but in fertilized and dividing egg cells this number is greater. mtDNA is much smaller, often containing fewer than 20,000 base pairs. The value for humans is 16,569 base pairs. The mtDNA is a circular duplex. mDNA codes for the mitochondrial tRNAs and rRNAs but only a fraction of the mitochondrial proteins. Over 95% of the mitochondrial proteins are encoded by nuclear DNA. The mitochondria divide when the cell divides. 

Phylogenetic relationship among cockroach families inferred from mitochondrial 12S rRNA gene sequence. Systematic Entomology 21 89-98. 

Mitochondrial DNA codes for the mitochondrial tRNAs and rRNAs and for a few mitochondrial proteins. More than 95% of mitochondrial proteins are encoded by nuclear DNA. Mitochondria and chloroplasts divide when the cell divides. Their DNA is replicated before and during division, and the daughter DNA molecules pass into the daughter organelles. 

A mutation in any of the 13 protein subunits, the 22 tRNAs, or the two rRNAs whose genes are carried in mitochondrial DNA may possibly cause disease. The 13 protein subunits are all involved in electron transport or oxidative phosphorylation. The syndromes resulting from mutations in mtDNA frequently affect oxidative phosphorylation (OXPHOS) causing what are often called "OXPHOS diseases."3-6 Mitochondrial oxidative phosphorylation also depends upon 100 proteins encoded in the nucleus. Therefore, OXPHOS diseases may result from defects in either mitochondrial or nuclear genes. The former are distinguished by the fact that they are inherited almost exclusively maternally. Most mitochondrial diseases are rare. However, mtDNA is subject to rapid mutation, and it is possible that accumulating mutants in mtDNA may be an important component of aging.h k... 

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