The Switch Regulating Transcription of the Escherichia coil Biotin Operon Does Not Require Extensive Protein-Protein Interactions

摘要

Transcription of the Escherichia coil biotin (bio)operon is regulated by BirA, a protein that is notonly the repressor that regulates bio operon expres-sion by DNA binding but also the enzyme that cova-lently attaches biotin to its cognate acceptorproteins. Binding of BirA to the bio operator requiresdimerization of the protein that is triggered by BirA-catalyzed synthesis of biotinoyl-adenylate (bio-AMP), the obligatory intermediate of the attachmentreaction. The current model postulates that theunmodified acceptor protein binds the monomericBirA:bio-AMP complex and thereby blocks assembly(dimerization) of the form of BirA that binds DNA. Wereport that expression of fusion proteins that carrysynthetic biotin-accepting peptide sequences wasas effective as the natural acceptor protein in dere-pression of bio operon transcription. These peptidesequences have sequences that are remarkablydissimilar to that of the natural acceptor protein,and our data thus argue that the regulatory switchdoes not require the extensive protein-protein inter-actions postulated in the current model.