In vitro transcription of pathogenesis-related genes by purified RNA polymerase from Staphylococcus aureus

The RNA polymerase (RNAP) holoenzyme of Staphylococcus aureus was purified by DNA affinity, gel filtration, and ion-exchange chromatography. This RNAP contained four major subunits with apparent molecular masses of 165, 130, 60, and 47 kDa. All four subunits of the RNAP were serologically related to the subunits of Escherichia coli E sigma 70 holoenzyme by Western immunoblot analysis. The 60-kDa subunit was subsequently isolated and found to react with a monoclonal antibody specific to the E. coli sigma 70 subunit. This sigma 70-related protein allowed E. coli core RNAP promoter-specific initiation and increased transcription by S. aureus RNAP that is unsaturated with sigma. We therefore suggest that this 60-kDa protein is a sigma factor. Purified S. aureus RNAP transcribed from the promoters of several important S. aureus virulence genes (sea, sec, hla, and agr P2) in vitro. The in vitro transcription start sites of the sea, sec, and agr P2 promoters, mapped by primer extension, were similar to those identified in vivo. The putative promoter hexamers of these three genes showed strong sequence similarity to the E. coli sigma 70 consensus promoter, and transcription by E sigma 70 from some of these promoters has been observed. Conversely, S. aureus RNAP does not transcribe from all E. coli sigma 70-dependent promoters. Taken together, our results indicate that the promoter sequences recognized by purified S. aureus RNAP are similar but not identical to those recognized by E. coli E sigma 70.