A CONSERVED DOMAIN WITHIN ARC1P DELIVERS TRANSFER-RNA TO AMINOACYL-TRANSFER-RNA SYNTHETASES

Two yeast enzymes that catalyze aminoacylation of tRNAs, MetRS and Glu RS, form a complex with the protein Arc1p. We show here that associati on of Arc1p with MetRS and GluRS is required in vivo for effective rec ruitment of the corresponding cognate tRNAs within this complex. Arc1p is linked to MetRS and GluRS through its amino-terminal domain, while its middle and carboxy-terminal parts comprise a novel tRNA-binding d omain. This results in high affinity binding of cognate tRNAs and incr eased aminoacylation efficiency. These findings suggest that Arc1p ope rates as a mobile, trans-acting tRNA-binding synthetase domain and pro vide new insight into the role of eukaryotic multimeric synthetase com plexes.