Association of cytochrome b translational activator proteins with the mitochondrial membrane: implications for cytochrome b expression in yeast.

The products of the nuclear genes CBS1 and CBS2 are both required for translational activation of mitochondrial apocytochrome b in yeast. We report the intramitochondrial localization of both proteins by use of specific antisera. Based on its solubilization properties the CBS1 protein is presumed to be a component of the mitochondrial membrane; the detergent concentrations needed to release CBS1 from mitochondria are almost the same as for cytochrome c1. In contrast, CBS2 behaves like a soluble protein, with some characteristics of a membrane-associated protein. A model is presented for translational activation of cytochrome b, which might also be applicable to translational regulation of other mitochondrial genes.