Ribosome specialization is an emerging concept which challenges the common assumption that translation relies on a standardized molecular machinery. In this work, we demonstrate that Tma108, a yeast uncharacterized translation machinery-associated factor, defines a subpopulation of the cellular ribosomes specifically involved in the translation of less than 200 mRNAs encoding proteins with ATP or zinc binding domains. Ribonucleoparticle dissociation experiments support the fact that Tma108 directly interacts with the nascent protein chain. Comparative genomic analyses and molecular modeling point out Tma108 as an original M1 metallopeptidase with specific residues in the catalytic pocket which may explain its selectivity. The involvement of Tma108 in co-translational regulations is attested by the drastic perturbation of the subcellular localization of ATP2 mRNA, one of its targets, upon TMA108 inactivation. Tma108 is an unique example of a nascent chain-associated factor with high selectivity and illustrates the existence of specific translation-associated factors, besides RNA binding proteins.