Characterization and submitochondrial localization of the a subunit of themitochondrial processing peptidase from the aquatic fungus Blastocladiellaemersonii

In an effort to investigate the molecular mechanisms responsible for the dr astic morphological changes the mitochondria go through during the life cyc le of the aquatic fungus Blastocladiella emersonii, the gene encoding the a lpha subunit of the mitochondrial processing peptidase (alpha-MPP) was isol ated. Nucleotide sequence analysis revealed that the predicted a-MPP polype ptide comprises 474 amino acids with a calculated molecular mass of 51,900 Da, presenting a characteristic mitochondrial signal sequence. Northern blo t analysis indicated a single 1.4-kb transcript encoding the B. emersonii a lpha-MPP, whose levels decrease during sporulation, becoming very low in th e zoospore, and increase again during germination. Despite these variations in mRNA concentration, B. emersonii alpha-MPP protein levels do not change significantly during the life cycle of the fungus, as observed in Western blots. Experiments to investigate the submitochondrial localization of B, e mersonii alpha-MPP and beta-MPP were also carried out, and the results indi cated that both subunits are associated with the mitochondrial inner membra ne, possibly as part of the bc1 complex, as described for plants.