In the elongator complex, acts as a tRNA uridine34 acetyltransferase by mediating formation of carboxymethyluridine in the wobble base at position 34 in tRNAs.May also act as a protein lysine acetyltransferase by mediating acetylation of target proteins; such activity is however unclear in vivo and recent evidences suggest that ELP3 primarily acts as a tRNA acetyltransferase.