RPON (SIGMA(54)) IS REQUIRED FOR CONVERSION OF PHENOL TO CATECHOL IN ACINETOBACTER-CALCOACETICUS

Members of the sigma(54) protein family, encoded by rpoN, are required for the transcription of genes associated with specialized metabolic functions. The ability to grow with phenol appears to be a specialized trait because it is expressed by few of the microorganisms that grow with catechol, the metabolic product of phenol monooxygenase. A mutati on preventing the expression of phenol monooxygenase in the bacterial strain Acinetobacter calcoaceticus NCIB8250 was complemented by wild-t ype DNA segments containing an open reading frame encoding a member of the sigma(54) protein family. DNA sequencing revealed a second open r eading frame, designated ORF2, directly downstream of A. calcoaceticus rpoN. The locations of both ORF2 and the 113-residue amino acid seque nce of its product are highly conserved in other bacteria. The mutatio n preventing the expression of rpoN results in an opal codon that term inates the translation of RpoN at a position corresponding to Trp-91 i n the 483-residue amino acid sequence of the wild-type protein. Negati ve autoregulation of rpoN was suggested by the fact that the mutation inactivating RpoN enhanced the transcription of rpoN. Primer extension revealed independent transcription start sites for rpoN and ORF2.