Cytochrome oxidase subunit VI of Trypanosoma brucei is imported without a cleaved presequence and is developmentally regulated at both RNA and protein levels

Mitochondrial respiration in the African trypanosome undergoes dramatic dev elopmental stage regulation. This requires co-ordinated control of componen ts encoded by both the nuclear genome and the kinetoplast, the unusual mito chondrial genome of these parasites. As a model for understanding the co-or dination of these genomes, we have examined the regulation and mitochondria l import of a nuclear-encoded component of the cytochrome oxidase complex, cytochrome oxidase subunit VI (COXVI). By generating transgenic trypanosome s expressing intact or mutant forms of this protein, we demonstrate that CO XVI is not imported using a conventional cleaved presequence and show that sequences at the N-terminus of the protein are necessary for correct mitoch ondrial sorting. Analyses of endogenous and transgenic COXVI mRNA and prote in expression in parasites undergoing developmental stage differentiation d emonstrates a temporal order of control involving regulation in the abundan ce of, first, mRNA and then protein. This represents the first dissection o f the regulation and import of a nuclear-encoded protein into the cytochrom e oxidase complex in these organisms, which were among the earliest eukaryo tes to possess a mitochondrion.