The processing peptidase of yeast mitochondria

Two proteins co-operate in the proteolytic cleavage of
mitochondrial precursor proteins: the mitochondrial processing
peptidase (MPP) and the processing enhancing protein (PEP). In
order to understand the structure and function of this novel
peptidase, we have isolated mutants of Saccharomyces cerevisiae
which were temperature sensitive in the processing of mitochondrial
precursor proteins. Here we report on the mif2 mutation which is
deficient in MPP. Mitochondria from the mif2 mutant were able to
import precursor proteins, but not to cleave the presequences. The
MPP gene was isolated. MPP is a hydrophilic protein consisting of
482 amino acids. Notably, MPP exhibits remarkable sequence
similarity to PEP. We speculate that PEP and MPP have a common
origin and have evolved into two components with different but
mutually complementing functions in processing of precursor
proteins.