THE RPON-BOX MOTIF OF THE RNA-POLYMERASE SIGMA-FACTOR SIGMA(N) PLAYS A ROLE IN PROMOTER RECOGNITION

The RNA polymerase sigma factor sigma(N) (sigma(54)) is characterized by the presence, near the C-terminal end of the protein, of a highly c onserved sequence of 10 amino acids (ARRTVAKYRE) that has been termed the RpoN box. In order to examine the function of this motif, which is predicted to adopt an alpha-helical stucture, we have isolated a numb er of mutations that alter residues within the box and examined the pr operties of the sigma(N) derivatives encoded by them. Certain mutation s that alter charged and potentially exposed residues within the motif result in transcriptionally inactive proteins with impaired promoter recognition but no impairment in core RNA polymerase binding. We there fore suggest that the RpoN box could play a direct or indirect role in recognition of the -24, -12 promoter consensus that is characteristic of sigma(N)-dependent genes.