Mitochondrial gene expression system involving extensive frameshift in a shellfish pathogen Perkinsus

Apicomplexan parasites are the causative agents of human infectious diseases including malaria. Modified metabolic pathways and unique gene expression systems of the parasites'mitochondria are promising drug targets. From an evolutionary viewpoint, in this study, I investigated mitochondria of Perkinsus, a relative of apicomplexans. The enrichment method for Perkinsus mitochondria was preliminarily established using Percoll density gradient ultracentrifugation. Perkinsus cells obviously showed enzyme activity ensuring the presence of the active mitochondrial electron-transport chain, and homologs of major subunits of mitochondrial electron-transport chain proteins of P. marinus were found from a public database. Although the sequence searches did not detect possible Perkinsus mitochondrial genes, I could determine the full-length mRNA sequence of cox1. Similar to apicomplexans, this gene lacked canonical start and stop codons in terminal regions. Curiously, this mRNA was not translated in a single reading frame with standard codon usage. Careful examination of the nucleotide sequence and its three-frame translation suggested that the reading frame must be shifted 10 times, at every AGG and CCC codon to yield a consensus COX1 protein. Two possible mechanisms were proposed for the frameshifts: ribosomal frameshifts in which stalled ribosomes skip the first bases of these codons or specialized tRNAs recognizing non-triplet codons, AGGY and CCCCU. Notably, this is the most extensive frameshift case described to date, which would utilize active and efficient machinery. It is valuable that this is a fundamental study on Perkinsus mitochondria and would provide evolutionary insights into mitochondrial functions of Perkinsus and their relatives including apicomplexans.

報告番号: 甲27141 ; 学位授与年月日: 2011-03-24 ; 学位の種別: 課程博士 ; 学位の種類: 博士(保健学) ; 学位記番号: 博医第3751号 ; 研究科・専攻: 医学系研究科国際保健学専攻