The role of the delta-lysin gene (hld) in the regulation of virulence genes by the accessory gene regulator (agr) in Staphylococcus aureus.

Abstract

The synthesis of at least 14 extracellular toxins and enzymes in Staphylococcus aureus is regulated by a set of trans‐acting elements from the agr (accessory gene regulator) locus. We have shown that the delta‐lysin gene (hld) that is transcribed from a promoter immediately upstream of the agr locus, and which is positively controlled by agr, is part of this regulatory system. Deletion replacement mutagenesis of the chromosomal hld gene had the same pleiotropic effect on the synthesis of several virulence factors as agrA mutations. Characteristically, these mutants had an almost complete block in the synthesis of alpha‐toxin, serin‐ and metalloprotease, whereas synthesis of protein A was greater than 10‐fold higher than in the parental strain. Corresponding changes in the levels of alpha‐toxin and protein A mRNAs were demonstrated by northern blotting experiments. The effects of the hld deletion mutation could be fully complemented by the hld gene on a plasmid. A plasmid insertion mutation in the 3′ non‐coding region of hld had a similar effect on exoprotein synthesis, indicating a role of the hld transcript in the regulation of exoprotein synthesis. This was confirmed by the finding that the effects of alpha‐toxin and protein A synthesis by the hld deletion replacement mutation could be fully complemented by a hld allele in which we had introduced an early stop codon in the delta‐lysin structural gene. However, the mutant hld allele could not complement the defect in production of extracellular proteases, indicating that delta‐lysin may act in conjunction with its mRNA to regulate the expression of some exoprotein genes.

Transcriptional occlusion caused by overlapping promoters

“…RpoS (σ 38 ) is required for cell survival under stress conditions, but it can inhibit growth if produced inappropriately and, consequently, its production and activity are elaborately regulated. Crl, a transcriptional activator that does not bind DNA, enhances RpoS activity by stimulating the interaction between RpoS and the core polymerase.…”

Crystal structure of the SarR protein from Staphylococcus aureus

“…RNAIII, initiated from the P3 promoter, is the regulatory molecule of the agr response, hence responsible for the up-regulation in extracellular protein production and the down-regulation of cell-wall-associated protein synthesis during the postexponential growth phase (5,6). The RNAII molecule, driven by the P2 promoter, encodes a four-gene operon, agrBDCA.…”

Cloning and sequencing of sarA of Staphylococcus aureus, a gene required for the expression of agr

“…The transposon Tn917 LTV1 inserted into the sar locus of the host chromosome contains an E. coli replicon carrying ampicillin as a selective marker (2). Taking Derivative of pC194 (15) (10) in E. coli XL-1 blue. Evidence that sarA is necessary for the optimal expression of agr.…”