BirA serves as both a transcriptional repressor and the enzyme
responsible for protein biotinylation (outlined in Fig. 1). As both biotin
ligase and transcriptional repressor activities are intimately linked,
we provide an overview of both functions as background for the
reader to understand the sophistication of this elegant system.
Protein biotinylation is achieved through a conserved, two-step re-
action mechanism that is catalyzed by biotin protein ligase (BPL)
in all organisms. In the first partial reaction biotin and ATP are re-
quired to form biotinyl-5′-AMP that serves as both the reaction