Mitochondrial membrane protein; effector of TORC1 signaling in a mitochondrial feedback loop that regulates cellular aging; transcriptionally up-regulated by TOR and inhibited by rapamycin treatment; deletion increases replicative and chronological life span; aging effects are HAP4- and RMD9-dependent; causes a synthetic respiratory defect in combination with rmd9 mutations; YBR238C has a paralog, RMD9, that arose from the whole genome duplication