SarA Represses agr Operon Expression in a Purified In Vitro Staphylococcus aureus Transcription System

Mutation and genetic complementation studies suggested that two chromosomal loci, agr and sar, are involved in the upregulation of several exotoxin genes and the downregulation of a number of surface protein genes in a growth phase-dependent manner in Staphylococcus aureus. We purified recombinant T7-tagged SarA from Escherichia coli and determined its effect on transcription from several S. aureus promoters by using purified RNA polymerase reconstituted with either ς(A) or ς(B) from S. aureus. Of the seven ς(A)-dependent promoters that we tested, SarA repressed transcription from agrP2, agrP3, cna, sarP1, and sea promoters and did not affect sec and znt promoters. Furthermore, SarA had no effect on transcription from the ς(B)-dependent sarP3 promoter. In vitro experimental data presented in this report suggest that SarA expression is autoregulated.