TIM23, A PROTEIN IMPORT COMPONENT OF THE MITOCHONDRIAL INNER MEMBRANE, IS REQUIRED FOR NORMAL ACTIVITY OF THE MULTIPLE CONDUCTANCE CHANNEL,MCC

We previously showed that the conductance of a mitochondrial inner mem brane channel, called MCC, was specifically blocked by peptides corres ponding to mitochondrial import signals. To determine if MCC plays a r ole in protein import, we examined the relationship between MCC and Ti m23p, a component of the protein import complex of the mitochondrial i nner membrane. We find that antibodies against Tim23p, previously show n to inhibit mitochondrial protein import, inhibit MCC activity. We al so find that MCC activity is altered in mitochondria isolated from yea st carrying the tim23-1 mutation. In contrast to wild-type MCC, we fin d that the conductance of MCC from the tim23-1 mutant is not significa ntly blocked by mitochondrial presequence peptides. Tim23 antibodies a nd the tim23-1 mutation do not, however, alter the activity of PSC, a presequence-peptide sensitive channel in the mitochondrial outer membr ane. Our results show that Tim23p is required for normal MCC activity and raise the possibility that precursors are translocated across the inner membrane through the pore of MCC.