CHARACTERIZATION OF A SAR HOMOLOG OF STAPHYLOCOCCUS-EPIDERMIDIS

Coagulase-negative staphylococci are common nosocomial pathogens. A re gulatory element, designated sar, partially controls exoprotein synthe sis in coagulase-positive Staphylococcus aureus by modulating the expr ession of another regulatory locus, called agr. We report here the clo ning of a sar homolog in S. epidermidis. The major open reading frame within sar in S. epidermidis is highly homologous (84%) to the S. aure us SarA protein. Primer extension studies revealed three sar transcrip ts (0.64, 0.76, and 0.85 kb) initiated from three distinct promoters. The interpromoter region in S. epidermidis differs from its S. aureus counterpart, possibly suggesting target gene differences and a dispara te pattern for sar activation. Remarkably, the S. epidermidis sar homo log interacts with an agr promoter fragment of S. aureus in gel shift assays. Additionally, S. epidermidis sar fragments could restore hemol ysin production in an S. aureus sar mutant. As typical virulence deter minants controlled by sar in S. aureus are not present in S. epidermid is, an examination of functional and structural similarities and diver gence of sar in staphylococci will be of major interest.