THE PROTEIN IMPORT RECEPTOR OF MITOCHONDRIA

Protein import into the mitochondria of Saccharomyces cerevisiae depen ds on two receptor subcomplexes composed of integral outer-membrane pr oteins. One subcomplex is the MAS37-MAS70 heterodimer, which preferent ially recognizes the mature regions of precursor proteins associated w ith ATP-dependent cytosolic chaperones. The other subcomplex contains the acidic proteins MAS20 and MAS22, which recognize the positively ch arged targeting sequences of a wide variety of mitochondrial precursor s. We propose that the two subcomplexes can act together as a single, multifunctional receptor that binds simultaneously to different region s of a precursor molecule.