Functional compatibility of elongation factors between mammalian mitochondrial and bacterial ribosomes: characterization of GTPase activity and translation elongation by hybrid ribosomes bearing heterologous L7/12 proteins

• Published in: Journal of molecular biology Vol. 336; no. 2; pp. 331 - 342
• Main Authors: Terasaki, Maki, Suzuki, Tsutomu, Hanada, Takao, Watanabe, Kimitsuna
• Format: Journal Article
• Language: English
• Published: England 13.02.2004
• Subjects: Amino Acid Sequence; Animals; Cattle; Enzyme Activation; Escherichia coli; Escherichia coli - enzymology; Escherichia coli Proteins - metabolism; Mammals; Mitochondria - enzymology; Mitochondrial Proteins - metabolism; Molecular Sequence Data; Peptide Chain Elongation, Translational; Peptide Elongation Factor G - metabolism; Peptide Elongation Factor Tu - metabolism; Protein Binding; Recombinant Fusion Proteins - metabolism; Ribosomal Proteins - metabolism; Ribosomes - chemistry; Ribosomes - metabolism
• ISSN: 0022-2836
• DOI: 10.1016/j.jmb.2003.12.034

The mammalian mitochondrial (mt) ribosome (mitoribosome) is a bacterial-type ribosome but has a highly protein-rich composition. Almost half of the rRNA contained in the bacterial ribosome is replaced with proteins in the mitoribosome. Escherichia coli elongation factor G (EF-G Ec) has no translocase activity on the mitoribosome but EF-G mt is functional on the E.coli ribosome. To investigate the functional equivalency of the mt and E.coli ribosomes, we prepared hybrid mt and E.coli ribosomes. The hybrid mitoribosome containing E.coli L7/12 (L7/12 Ec) instead of L7/12 mt clearly activated the GTPase of EF-G Ec and efficiently promoted its translocase activity in an in vitro translation system. Thus, the mitoribosome is functionally equivalent to the E.coli ribosome despite their distinct compositions. The mt EF-Tu-dependent translation activity of the E.coli ribosome was also clearly enhanced by replacing the C-terminal domain (CTD) of L7/12 Ec with the mt counterpart (the hybrid E.coli ribosome). This strongly indicates that the CTD of L7/12 is responsible for EF-Tu function. These results demonstrate that functional compatibility between elongation factors and the L7/12 protein in the ribosome governs its translational specificity.