TRANSCRIPTION PROPERTIES OF RNA-POLYMERASE HOLOENZYMES ISOLATED FROM THE PURPLE NONSULFUR BACTERIUM RHODOBACTER-SPHAEROIDES

We have been characterizing RNA polymerase holoenzymes from Rhodobacter sphaeroides. RNA polymerase purified from R. sphaeroides transcribed from promoters recognized by Escherichia coli E sigma(32) or E sigma(70) holoenzyme. Antisera to E. coli sigma(32) or sigma(70) indicated that related polypeptides of approximate to 37 kDa (sigma(37)) and 93 kDa (sigma(93)), respectively, are present in this preparation. Transcription of sigma(32)-dependent promoters was observed in a further fractionated R. sphaeroides holoenzyme containing the sigma(37) polypeptide, while a preparation enriched in sigma(93) transcribed sigma(70)-dependent promoters. To demonstrate further that the sigma(93) polypeptide functions like E. coli sigma(70), we obtained an R. sphaeroides E sigma(93) holoenzyme capable of transcription from sigma(70)-dependent promoters by combining sigma(93) with (i) an E sigma(37) fraction with diminished sigma(93) polypeptide content or (ii) E. coli core RNA polymerase. The generation of analogous DNase I footprints on the lacUV5 promoter by R. sphaeroides E sigma(93) and by E. coli E sigma(70) suggests that the overall structures of these two holoenzymes are similar. However, some differences in promoter specificity between R. sphaeroides E sigma(93) and E. coli E sigma(70) exist because transcription of an R. sphaeroides rRNA promoter was detected only with E sigma(93).