Cbp1 is required for translation of the mitochondrial cytochrome b mRNA of Saccharomyces cerevisiae

Expression of the yeast mitochondrial cytochrome b gene (COB) is controlled by at least 15 nuclear-encoded proteins. One of these proteins, Cbp1, is required for COB mRNA stability. Δcbp1 null strains fail to accumulate mature COB mRNA and cannot respire. Since Δcbp1 null strains lack mature COB transcripts, the hypothesis that Cbp1 also plays a role in translation of these mRNAs could not be tested previously. 5′-End trimming of precursor COB RNA and other mitochondrial transcripts is dependent on Pet127. pet127 mutants accumulate high levels of precursor COB mRNA and have no mature mRNA. pet127 mutants respire well; this phenotype implies that COB precursor RNA is translated efficiently. With the expectation that a Δcbp1Δpet127 strain might accumulate substantial levels of COB RNA, the double null strain was constructed and analyzed to test the hypothesis that Cbp1 is required for translation of COB RNA. The Δcbp1Δpet127 strain does accumulate levels of COB precursor mRNA that are ∼60% of the level of COB mRNA in the wild-type strain. However, cytochrome b protein is not synthesized, and thus the Δcbp1Δpet127 strain does not respire. These results suggest that Cbp1 is required for translation of COB RNAs.