title: Strengthened arm-dimerization domain interactions in AraC.
abstract: Constitutive mutations were sought and found in the N-terminal arm of the Escherichia coli regulatory protein of the arabinose operon, AraC protein. A new mutation, N16D, was of particular interest. Asn-16 is not seen in the crystal structure of the AraC dimerization domain determined in the absence of arabinose, because the N-terminal arm 18 residues are disordered, but in the presence of arabinose, residues 7-18 fold over the arabinose and make many interactions with it. In this state Asn-16 lies near two positively charged amino acids, Lys-43 and Arg-99. We propose that the introduction of the negatively charged aspartic residue at position 16 creates a charge-charge interaction network among Asp-16, Lys-43, and Arg-99 that holds the arm to the dimerization domain even in the absence of arabinose. This frees the DNA-binding domains and allows them to bind cis to I(1)-I(2) half-sites and activate transcription. Mutating the two positively charged residues to alanines individually and collectively decreased or eliminated the constitutivity created by the N16D mutation.
authors.affiliation: Biology Department, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: M
authors.initials: M
authors.lastname: Wu
authors.forename: R
authors.initials: R
authors.lastname: Schleif
mesh_terms: D051777:AraC Transcription Factor; D001089:Arabinose / Q000378:metabolism*; D001120:Arginine; D001224:Aspartic Acid; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D008239:Lysine; D008957:Models, Genetic; D009154:Mutation; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors
chemical_list: D051777:AraC Transcription Factor; C497371:AraC protein, E coli; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D001224:Aspartic Acid; D001120:Arginine; D001089:Arabinose; D008239:Lysine