Studies on the expression of regulatory locus sae in Staphylococcus aureus

Global regulatory locus sae consists of a two-component signal transduction system coded by saeR and saeS genes that upregulates the transcription of several exoproteins. Northern analysis carried out in this study reveals the synthesis at late and post-exponential phases of a cotranscript of saeR and saeS structural genes of about 2.4 kb. This transcript is diminished in the isogenic agr::tetM mutant. Likewise, transcriptional fusion experiments show that sae expression is downregulated in the agr null mutant. Complementation analyses with plasmids carrying fragments of about 1.2 or 0.2 kbp upstream of saeR-saeS genes, which restore fully or only partially, respectively, the wild-type phenotype to the sae mutant, are in agreement with two initiation start points of transcription revealed by primer extension experiments. This work, as well as previous studies, reveals a complex hierarchical regulatory network involving several loci that control the expression of virulence determinants in S. aureus.