THE SAE LOCUS OF STAPHYLOCOCCUS-AUREUS CONTROLS EXOPROTEIN SYNTHESIS AT THE TRANSCRIPTIONAL LEVEL

Agr and sar are known regulatory loci of Staphylococcus aureus that co ntrol the production of several extracellular and cell-wail-associated proteins. A pleiotropic insertional mutation in S. aureus, designated sae, that leads to the production of drastically diminished levels of alpha- and beta-hemolysins and coagulase and slightly reduced levels of protein A has been described. The study of the expression of the ge nes coding for these exoproteins in the sae::Tn551 mutant (carried out in this work by Northern blot analyses) revealed that the genes for a lpha- and beta-hemolysins (hla and hlb) and coagulase (coa) are not tr anscribed and that the gene for protein A (spa) is transcribed at a so mewhat reduced level. These results indicate that the sae locus regula tes these exoprotein genes at the transcriptional level. Northern blot analyses also show that the sae mutation does not affect the expressi on of agr or sar regulatory loci. An sae::Tn551 agr::tetM double mutan t has been phenotypically characterized as producing reduced or null l evels of alpha-, beta-, and delta-hemolysins, coagulase, and high leve ls of protein A. Northern blot analyses carried out in this work with the double mutant revealed that hla, hlb, hld, and coa genes are not t ranscribed, while spa is transcribed at high levels. The fact that coa is not expressed in the sae agr mutant, as in the sae parental strain , while spa is expressed at the high levels characteristic of the agr parental strain, suggests that sae and agr interact in a complex way i n the control of the expression of the genes of several exoproteins.