BirA Biotin-protein ligase (EC 6.3.4.15) activates biotin to form biotinyl 5'-adenylate and transfers the biotin to biotin-accepting proteins (such as AviTag™ peptide). It also functions as a biotin operon repressor. The protein is encoded by the birA gene. Please Note: We strongly recommend the use of the AviTag™ amino acid sequence over other Biotinylation of Peptides sequences. The BirA enzyme biotinylates the AviTag™ sequence at a reaction rate 2x the natural substrate (BCCP) and as much as an order of magnitude or more over the other peptide sequences in use. The AviTag™ requires smaller amounts of enzyme and shorter incubation times than other Biotinylation-of-Peptides sequences thus minimizing ancillary problems associated with proteases and protein instability.