(GenBank) bifunctional: biotin-[acetylCoA carboxylase] holoenzyme synthetase; transcriptional repressor of biotin synthesis (BirA family) BirA acts both as a biotin-operon repressor and as the enzyme that synthesizes the corepressor, acetyl-CoA:carbon-dioxide ligase. This protein also activates biotin to form biotinyl-5'-adenylate and transfers the biotin moiety to biotin-accepting proteins