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

Abstract

ABSTRACT 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 agr P2, agr P3, cna , sar P1, and sea promoters and did not affect sec and znt promoters. Furthermore, SarA had no effect on transcription from the ς B -dependent sar P3 promoter. In vitro experimental data presented in this report suggest that SarA expression is autoregulated.