Catalytic tRNA acetyltransferase subunit of the elongator complex which is required for multiple tRNA modifications, including mcm5U (5-methoxycarbonylmethyl uridine), mcm5s2U (5-methoxycarbonylmethyl-2-thiouridine), and ncm5U (5-carbamoylmethyl uridine) (By similarity). In the elongator complex, acts as a tRNA uridine(34) acetyltransferase by mediating formation of carboxymethyluridine in the wobble base at position 34 in tRNAs (By similarity). Plays a role in the control of synaptic bouton expansion (PubMed:20626565). Required for larval development (PubMed:21288872). acetyl-CoA + H2O + S-adenosyl-L-methionine + uridine(34) in tRNA = 5'-deoxyadenosine + carboxymethyluridine(34) in tRNA + CoA + 2 H(+) + L-methionine Binds 1 [4Fe-4S] cluster. The cluster is coordinated with 3 cysteines and an exchangeable S-adenosyl-L-methionine. tRNA modification; 5-methoxycarbonylmethyl-2-thiouridine-tRNA biosynthesis. Component of the elongator complex. Pronounced larval developmental delay and death at the pupal stage with delayed and reduced ecdysone-induced transcription, developmental of melanotic nodules and up-regulation of stress-induced genes (PubMed:21288872). RNAi-mediated knockdown results in lethality at the late pupal stage (PubMed:20626565). RNAi-mediated knockdown in the central nervous system results in a hyperactive phenotype, sleep loss in adult females, a significant expansion in synaptic bouton number in the larval neuromuscular junction (NMJ), increased larval NMJ axonal length and branching, and misregulation of genes known to be involved in these processes with a marked increase in Hsc70-3 and Syb mRNA levels and a marked decrease in qvr/sss mRNA levels (PubMed:20626565). RNAi-mediated knockdown in hemocytes results in reduced hemocyte numbers and hemocyte aggregation (PubMed:21288872). Belongs to the ELP3 family. The elongator complex was originally thought to play a role in transcription elongation. However, it is no longer thought to play a direct role in this process and its primary function is thought to be in tRNA modification.