Leucyl-tRNA synthetase (LeuRS) is responsible for the LeU-tRNA(Leu) synthesis. The connective peptide 1 (CP1) domain inserted into the Rossmann nuclecitide binding fold possesses editing active site to hydrolyze the mischarged tRNA(Leu) with noncognate amino acid, then to ensure high fidelity of protein synthesis. A few co-crystal structures of LeuRS with tRNA(Leu) in different conformations revealed that tRNA(Leu) 3' end shuttled between synthetic and editing active sites dynamically with direct and specific interaction with the CP1 domain. Here, we reported that Y515 and Y520 outside the editing active site of CP1 domain of Giardia lamblia LeuRS (G/LeuRS) are crucial for post-transfer editing by influencing the binding affinity with mischarged tRNA. Mutations on Y515 and Y520 also decreased tRNA(Leu) charging activity to various extents but had no effect on leucine activation. Our results gave some biochemical knowledge about interaction of tRNA(Leu) 3' end with the CP1 domain in archaeal/eukaryotic LeuRS. (C) 2009 Elsevier Inc. All rights reserved.