Mitochondrial protein-coding genes

Table 3.2. Divergence (%) in 12 mitochondrial protein-coding genes (nucleotide sequence (above diagonal) and amino acid sequence (below diagonal)) and in nucleotide sequences of the mitochondrial large (rrnL) (above diagonal) and small (rrnS) (below diagonal) ribosomal RNA (rRNA) subunits between the sheep-dog (EgG1) and horse-dog (EgG4) strains of Echinococcus granulosus, E. multilocularis (Em) and Taenia crassiceps (Tc). (After Le ef a/., 2002.)...

Higher-level vertebrate phylogenies based on mitochondrial protein-coding genes (concatenated) have differed almost completely from those based on morphology and... 

Point Mutations in Protein-Coding Genes of mtDNA Associated with Mitochondrial Diseases 1... 

Yet, this genome encodes less than 2% of the protein-coding genes in the bacterium E. coli. It seems unlikely that mitochondrial genomes resulting from several endosymbiotic events could have been independently reduced to the same set of genes found in R. americana. 

Eukaryotic RNA polymerases are less well-characterized than the bacterial enzyme. Biochemical studies have so far identified three distinct nuclear RNA polymerase activities in eukaryotic cell extracts prepared from both yeast and human cells. These RNA polymerases, referred to as RNA pol I, RNA pol II, and RNA pol HI, each contain a large number of subunits, some of which appeared to be shared between the different RNA polymerase subtypes. As shown in Table 24.1, RNA pol I transcribes ribosomal RNA genes, RNA pol II transcribes the majority of protein-coding genes, into mRNA, and RNA pol III transcribes tRNA, small nuclear RNAs (snRNAs), and ribosomal 5S genes. Note also that the mitochondrial genome is transcribed by a nuclear-encoded mitochondrial RNA polymerase. The yeast mitochondrial RNA polymerase holoenzyme consists of a 140-kd catalytic subunit and a 43-kd promoter-recognition protein similar to the bacterial s factor. 

Not all the cellular DNA is in the nucleus some is found in the mitochondria. In addition, mitochondria contain RNA as well as several enzymes used for protein synthesis. Interestingly, mitochond-rial RNA and DNA bear a closer resemblance to the nucleic acid of bacterial cells than they do to animal cells. For example, the rather small DNA molecule of the mitochondrion is circular and does not form nucleosomes. Its information is contained in approximately 16,500 nucleotides that func-tion in the synthesis of two ribosomal and 22 transfer RNAs (tRNAs). In addition, mitochondrial DNA codes for the synthesis of 13 proteins, all components of the respiratory chain and the oxidative phosphorylation system. Still, mitochondrial DNA does not contain sufficient information for the synthesis of all mitochondrial proteins most are coded by nuclear genes. Most mitochondrial proteins are synthesized in the cytosol from nuclear-derived messenger RNAs (mRNAs) and then transported into the mito-chondria, where they contribute to both the structural and the functional elements of this organelle. Because mitochondria are inherited cytoplasmically, an individual does not necessarily receive mitochondrial nucleic acid equally from each parent. In fact, mito-chondria are inherited maternally. 

Sukhdeo, S.C., Sukhdeo, M.V.K., Black, M.B. and Vrijenhoek, R.C. (1997) The evolution of tissue migration in parasitic nematodes (Nematoda Strongylida) inferred from a protein-coding mitochondrial gene. Biological Journal of the Linnean Society 61, 281—298. 

Williams BA, Keeling PJ (2005) Microsporidian mitochondrial proteins expression in Antonospora locustae spores and identification of genes coding for two further proteins. J Eukaryot Microbiol 52 271-276... 

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