Bovine mitochondrial ribosomes. Elongation factor specificity.

The activity of bovine mitochondrial ribosomes with elongation factors from a variety of sources including the mitochondria of lower eukaryotes, chloroplasts, Gram-negative bacteria, Gram-positive bacteria, and the eukaryotic cell cytoplasm has been investigated. Bovine mitochondrial ribosomes are active with homologous mitochondrial elongation factor (EF)-G but display no activity with the mitochondrial or chloroplast translocases from the lower eukaryote Euglena gracilis, with Escherichia coli or Bacillus subtilis EF-G or with cytoplasmic EF-2. In contrast to the results obtained with the translocases, E. coli EF-Tu, B. subtilis EF-Tu, and Euglena chloroplast EF-Tu all function to a significant extent on the mitochondrial ribosomes. Cytoplasmic EF-1 has barely detectable activity on the animal mitochondrial ribosomes. The polymerization of phenylalanine by these ribosomes is dependent on poly(U), displays a rather broad Mg2+ optimum around 12 mM, and proceeds most rapidly at low monovalent ion concentrations.