Nuclearly-encoded CBP1 interacts with the 5' end of mitochondrial cytochrome b pre-mRNA.

CBP1 is a nuclearly-encoded protein that is imported into mitochondria and confers stability on the mRNA for cytochrome b. Previous work has shown that CBP1 interacts with the cytochrome b transcript upstream of the coding sequence; a region encompassing some 1,100 nucleotides. The work presented here narrows the site of action of CBP1 to the distal third of this upstream sequence through analysis of mRNA produced from a novel recombinant gene containing segments of the gene for cytochrome b, cob, and the ATP synthase subunit 9 gene, olil. In a wild-type CBP1 strain, the cob-olil-cob gene produces stable, mature mRNA that is translated and contributes a portion of the cytochrome b necessary for optimal growth on non-fermentable medium.