THE MOLECULAR ARCHITECTURE OF THE SAR LOCUS IN STAPHYLOCOCCUS-AUREUS

The global regulator sar in Staphylococcus aureus controls the synthes is of a variety of cell wall and extracellular proteins, many of which are putative virulence factors. The sar locus in strain RN6390 contai ns a 339-bp open reading frame (sarA) and an 860-bp upstream region, T ranscriptional analyses of this Locus revealed three different transcr ipts of 0.58, 0.84, and 1.15 kb (designated sarA, sarC, and sarB, resp ectively). All three transcripts seemed to be under temporal, growth c ycle-dependent regulation, with sarA and sarB being most abundant in e arly log phase and the sarC concentration being highest toward the lat e stationary phase. Mapping of the 5' ends of the sar transcripts by p rimer extension and modified S1 nuclease protection assays demonstrate d that transcription is initiated from three separate, widely spaced p romoters, The 3' ends of all three sar transcripts are identical, and transcriptional termination occurs upstream of a typical prokaryotic p oly(T) termination signal. Northern (RNA) analysis of sar mutant clone s containing plasmids that comprised various promoters and the termina tion signal revealed that individual transcripts can be generated from each of the three promoters, thus suggesting possible activation as i ndependent promoters. The multipromoter system, from which transcripti on is initiated, bears conserved features for recognition by homologou s sigma(70) transcription factors and also by those expressed in the g eneral stress response. Downstream of the two distal promoters (P3 and P2) are two regions potentially encoding short peptides. It is concei vable that posttranslational cooperation between these short peptides and the sarA gene product occurs to modulate sar-related functions. Co mplementation studies of a sar mutant with a clone expressing all thre e sar transcripts showed that this clone was able to restore the sar w ild-type phenotype to the sar mutant.