Catalyzes the formation of N(4)-acetylcytidine (ac(4)C) at the wobble position of tRNA(Met), by using acetyl-CoA as an acetyl donor and ATP (or GTP). It recognizes the wobble base of tRNA(Met), thus distinguishing between tRNA(Met) and the structurally similar tRNA(Ile2) (PubMed:18668122, PubMed:19322199). Could use an RNA helicase motor driven by ATP hydrolysis to deliver the wobble base of tRNA(Met) to the acetyltransferase domain of TmcA (Probable). Also functions as a lysine 2-hydroxyisobutyryltransferase to regulate transcription. Can specifically catalyze the 2-hydroxyisobutyrylation (Khib) of the DNA-binding protein H-NS. Hydroxyisobutyrylation of H-NS decreases its DNA-binding activity, promotes the expression of acid-resistance genes and enhances bacterial survival under extreme acid stress. acetyl-CoA + ATP + cytidine(34) in elongator tRNA(Met) + H2O = ADP + CoA + H(+) + N(4)-acetylcytidine(34) in elongator tRNA(Met) + phosphate 2-hydroxyisobutanoyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-(2-hydroxyisobutanoyl)-L-lysyl-[protein] ATP/GTP hydrolysis is stimulated by the addition of acetyl-CoA and tRNA(Met). Binding of acetyl-CoA to TmcA activates both ATPase and tRNA-binding activities (PubMed:18668122, PubMed:19322199). ATP promotes the 2-hydroxyisobutyryltransferase activity (PubMed:34903851). Mutants lack the ac(4)C modification, but do not show any growth defects (PubMed:18668122). Knockout mutant shows decreased 2-hydroxyisobutyrylation levels (PubMed:34903851). 467 endogenous Khib candidate sites significantly regulated by TmcA were identified in E.coli using a quantitative proteomics approach. Belongs to the RNA cytidine acetyltransferase family. TmcA subfamily.