Intermolecular Network specific for mitochondrial translation systems and its functional characteristics

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The genetic information translation system of animal mitochondria possesses the following remarkable characteristics as compared with that of prokaryote. (1) There exist T arm-lacking tRNA and a specific translation factor EF-Tu with a long C terminal region, recognizing this type of tRNA in nematode mitochondria. (2) There exist aminoacyl-tRNA synthetases which recognize all types of tRNA independent of the species including the tRNAs. (3) Mitochondrial ribosomes are functionally equivalent to E. coil ribosomes, although the ratio of content of RNAs and proteins is reversed. ; the ratio of content of RNAs and proteins is 2:1 in E. coliribosomes and that of animal mitochondria is 1:3. Through analyses of intermolecular network of these components, the construction principal of the genetic information translation system, which constitutes the root of the living phenomena, was investigated, and the following results were obtained.(1) There exist 2 species of EF-Tu in nematode mitochondri … More a, one (EF-Tu1) recognizing the T arm-lacking tRNA, the other (EF-Tu2 ) recognizing the D arm-lacking seryl-tRNA. EF-Tu1 recognizes not only tRNA structure but also serine residue attached to the tRNA. The amino acid residues involved in these recognitions were identified. The m^1A9 residue commonly existing in the T-arm-lacking tRNAs is indispensable for the binding of tRNA to EF-Tu1.(2) Mitochondrial seryl-tRNA synthetases recognize 2 structurally different serine tRNAs. The enzyme is very similar to that of E. coli in a total structure, but possesses extra two domains, an α-helical region at the N terminal and a tail region at the C terminal These two domains possess indispensable role in recognizing the D stem-lacking serine tRNA. Since a clear difference has been observed in amino acid residues involved in recognition of 2 structurally different tRNAs, it was deduced that this enzyme recognizes these 2 types of tRNA by quite different manner (dual mode recognition).(3) Mitochondrial (mt) EF-G can function on E. coli ribosome, on the other hand, E. coli EF-G cannot function on mitochondrial ribosome. It turned out that the difference was originated in the difference in only a stalk protein of ribosome, L7/L12. Less