One of two mitochondrially-localized peptidyl-tRNA hydrolases; ubiquitin-like (UBL) domain binding protein that negatively regulates the Ub-proteasome pathway via interactions with Rad23p and Dsk2p, UBL-ubiquitin-associated proteins; delays protein translocation into the mitochondrial matrix to protect mitochondria from toxic CAT-tailed proteins during the mitochondrial ribosome quality-control pathway; dispensable for cell growth; see also PTH1