The alternative sigma factor sigma(28) of the extreme thermophile Aquifex aeolicus restores motility to an Escherichia coli fliA mutant

Sigma factor sigma(28) (sigma(F), FliA, SigD) directs RNA polymerase to tra nscribe the genes required for flagellar biosynthesis and chemotaxis in man y bacteria. including Bacillus Subtilis, Legionella pneumophila. Salmonella typhimurium, Escherichia coli, Yersinia enterolytica, Treponema maltophilu m and Pseudomonas aeruginosa. Remarkably the fliA gene from the extreme the rmophile Aquifex aeolicus restored motility to the E. coli mutant at relati vely low temperature, albeit partially. This clearly demonstrates that A. a eolicus sigma(28)S is able to direct RNA polymerase to E. coli sigma(28)-de pendent promoters and take part in the complex interactions required to sup port transcription of the flagellar apparatus in vivo. The ability of A. ac olicus sigma(28) to function with mesophilic components shows that critical functional interactions made by these sigma factors are well conserved, an d are not dependent upon high temperature. We over-produced and purified th e sigma(28) protein and demonstrated binding to E. coli core RNA polymerase in vitro. In common with SigD from B, subtilis, but unlike most sigma fact ors, ii, aeolicus sigma(28) showed DNA binding activity in vitro but there was no evidence of sequence specificity. We note that A. aeolicus sigma(28) is a good candidate for structural studies. (C) 2000 Federation of Europea n Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.