Mutational analysis of the PapB transcriptional regulator in Escherichia coli - Regions important for DNA binding and oligomerization

PapB transcriptional regulator in the control of pop operon expression in E scherichia coli. There are PapB homologous proteins encoded by many fimbria l gene systems that are involved in the regulation of fimbriae-adhesin prod uction, and previous studies suggested that PapB binds DNA through minor gr oove contact. Both deletion and alanine-scanning mutagenesis were used to i dentify functionally important regions of the PapB protein. Mutations alter ing Arg(61) or Cys(65) caused deficiency in DNA binding, indicating that th ese residues are critical for PapB binding to DNA Alanine substitutions at positions 35-36, 53-56, and 74-76 resulted in mutants that were impaired in oligomerization. All these amino acid residues are conserved among the Pap B homologous proteins, suggesting their importance in the whole family of r egulatory proteins, The transcriptional efficiency of all the mutants was c learly reduced as compared with that of wild-type PapB. Taken together, we have localized regions in the PapB protein that are involved in DNA binding and oligomerization, and our results show that both functions are required for its activity as a transcriptional regulator.