Molecular Characterization of a NovelStaphylococcus aureusSerine Protease Operon

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Abstract
The present study identified and characterized a unique operon (spl) encoding six serine protease-like proteins. In addition, native Spl proteins were isolated and characterized. Typical of most exoproteins, thesplgene products contain putative 35- or 36-amino-acid signal peptides. The Spl proteins share 44 to 95% amino acid sequence identity with each other and 33 to 36% sequence identity with V8 protease. They also contain amino acids found in catalytic triads of enzymes in the trypsin-like serine protease family, and SplB and SplC were shown to degrade casein. Thesploperon is transcribed on a 5.5-kb transcript, but several nonrandom degradation products of this transcript were also identified. Similar to otherS. aureusexoprotein genes, thesploperon is maximally expressed during the transition into stationary phase and is positively controlled by the Agr virulence factor regulator. The Sar regulatory system did not affectsploperon expression. PCR analysis revealed the presence of thesploperon in 64% of theS. aureusisolates tested, although onesploperon-negative isolate was shown to contain at least two of thesplgenes. Finally, intraperitoneal injection of ansploperon deletion mutant revealed no major differences in virulence compared to the parental strain.