Identification ofsarV(SA2062), a New Transcriptional Regulator, Is Repressed by SarA and MgrA (SA0641) and Involved in the Regulation of Autolysis inStaphylococcus aureus

Abstract

The expression of genes involved in the pathogenesis of Staphylococcus aureus is known to be controlled by global regulatory loci, including agr, sarA, sae, arlRS, lytSR, and sarA-like genes. Here we described a novel transcriptional regulator called sarV of the SarA protein family. The transcription of sarV is low or undetectable under in vitro conditions but is significantly augmented in sarA and mgrA (norR or rat) (SA0641) mutants. The sarA and mgrA genes act as repressors of sarV expression, as confirmed by transcriptional fusion and Northern analysis data. Purified SarA and MgrA proteins bound specifically to separate regions of the sarV promoter as determined by gel shift and DNase I footprinting assays. The expression of 19 potential target genes involved in autolysis and virulence, phenotypes affected by sarA and mgrA, was evaluated in an isogenic sarV mutant pair. Our data indicated that the sarV gene product played a role regulating some virulence genes and more genes involved in autolysis. The sarV mutant was more resistant to Triton X-100 and penicillininduced lysis compared to the wild type and the sarA mutant, whereas hyperexpression of sarV in the parental strain or the sarV mutant rendered the resultant strain highly susceptible to lysis. Zymographic analysis of murein hydrolase activity revealed that inactivation of the sarV gene results in decreased extracellular murein hydrolase activity compared to that of wild-type S. aureus. We propose that sarV may be part of the common pathway by which mgrA and sarA gene products control autolysis in S. aureus.

Structural and function analyses of the global regulatory protein SarA from Staphylococcus aureus

“…2). The notion of a SarA multimer in binding to DNA was also supported by results of gel-retardation assays, showing a large mobility shift of the protein-DNA complex (9,11,12,(22)(23)(24). It will be of interest to understand how these multiple homodimers bind to their target DNA and their association with each other.…”

“…A search of the recently released S. aureus genomes revealed at least 10 additional SarA homologs, six of which have been partially characterized. These members include SarR, SarS, SarT, SarU, SarV, and MgrA (also called Rat) (12)(13)(14)(15)(16). Members of the SarA protein family also share sequence homology with the MarR protein or homologs in Gram-negative bacteria (13).…”

“…The sarA locus is composed of three overlapping transcripts, sarA P1, sarA P3, and sarA P2, each encoding the major 372-bp sarA ORF that yields the 14.7-kDa SarA protein (5). DNase I footprinting studies revealed that the SarA protein binds to several target gene promoters (9), including those of agr, hla, spa, and fnbA, thus implicating SarA to be a DNA-binding protein that can modulate target gene transcription via both agrdependent and agr-independent pathways (9)(10)(11)(12).…”

Regulation of Rot Expression in Staphylococcus aureus

“…SarX is a negative regulator of Agr (17). MgrA has been shown to be an activator of microcapsule synthesis, nuclease expression, and norA transcription but represses the expression of alpha-toxin, coagulase, protease, protein A, and certain genes involved in autolysis (11,18,39).Rot was identified as a negative transcription regulator of alpha-hemolysin and protease expression (20 genes repressed by Rot (32). The regulation of Rot production is not well understood.…”

“…SarU is proposed to be a positive regulator of agr expression (16). SarV is thought to be an important regulator in the autolytic pathway of S. aureus (18). SarX is a negative regulator of Agr (17).…”