Mutational analysis of yeast mitochondrial translational activator Cbs2p and of YHR063Cp, a protein with similarity to Cbs2p.

Translation of mitochondrial cytochrome b in Saccharomyces cerevisiae requires the nuclearly encoded proteins Cbs1p, Cbs2p and Cbp6p. So far no homologs have been identified, except for the product of the S. cerevisiae orf YHR063C, which has some similarity to Cbs2p. Here we analyze the effect of a null mutation of YHR063C and show that it is not required for mitochondrial respiration. In addition, we report on the importance of the carboxyl-terminus of Cbs2p for its function. We show that truncations and some directed mutations in the carboxyl-terminal region of Cbs2p render the protein non-functional. The importance of the COOH-terminus is further underscored by the finding that mutational alteration of the cbs2-1 allele results in the substitution of Ile(372) by Lys.