| Research Abstract |
This research project aims to elucidate the basal principle by which the translation system is constituted and functions, by analyzings the, functional structures of the ribosome and ribosomal RNA (rRNA). Since the translation system is the most basic system in life, elucidation of its constitution principle would lead to elucidation of origin of life.
In the beginning of this research, we tried to elucidate each step in the translation reaction using protein-deprived ribosomes treated with pyridine for the, purpose of elucidating the functional structure of E. coli ribosomes and rRNA. It turned out that such ribosomes possess non-enzymatic (spontaneous) translocation activity.
However, in these two years X-ray analysis of ribosome crystals has been greatly improved and it became possible to elucidate the reaction mechanism of ribosomes by inspection of the three-dimensional structure of ribosomes at atomic level. We thus moved our research target from E. coli to animal mitochondrial rib
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osomes, because mitochondrial ribosomes possess about a half-shortened rRNA and instead, doubly enlarged proteins, while the molecular weight and whole size being similar, as compared to those of E. coli ribosomes, suggesting that the identification of functional sites in rRNA is much easier and moreover, the roles of RNA could have transferred to proteins during evolution of mitochondria.
We have already identified 55 ribosomal proteins out of about 70 proteins in bovine, mitochondrial ribosome (mitoribosome) by separating each ribosomal, protein, on the two-dimensional gel electrophoresis followed by its identification by LC/MS technique. We are now characterizing these proteins. It also turned out that a hybrid-type mitoribosome in which only L7/L12 protein was replaced by the E. coli counterpart can function either with a set of mitochondrial tRNA and translation factors or with a set of E. coli tRNA and translation factors, suggesting that the most part of the ribosome is functionally equivalent between E. coli and mitochondrial ribosomes, notwithstanding that the RNA-protein ratio is reversed. We are also examining the origin of this functional interchangeability between E. coli and mitochondrial ribosomes. Less
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