TRANSCRIPTION ANALYSIS OF THE STAPHYLOCOCCUS-AUREUS GENE ENCODING PENICILLIN-BINDING PROTEIN-4

The high level of cross-linking found in Staphylococcus aureus peptido glycan is dependent on the low-molecular-weight penicillin-binding pro tein PBP4. Recently, the PBP4 gene, pbpD, was cloned and shown to be a djacent to and divergently transcribed relative to the putative ABC-ty pe transporter gene, abcA. Disruption of abcA (in strain KB400) was pr eviously shown to result in heightened resistance to several antibioti cs known to interact with PBP4, suggesting that the regulation of pbpD is affected by abcA. In this report, this hypothesis was confirmed by use of a Northern (RNA) blot analysis which revealed increased accumu lation of pbpD-specific transcripts in KB400 compared to that in the w ild-type strain, 8325-4. By using reverse-phase highperformance liquid chromatography to examine the structure of the peptidoglycan, it was demonstrated that the increased expression of pbpD resulted in an incr eased level of peptidoglycan cross-linking in the staphylococcal cell wall, Promoter fusion studies demonstrated that the abcA mutation caus ed approximately 7-fold and 100-fold increases in pbpD and abcA promot er activities, respectively, Primer extension experiments revealed tha t these genes have long, untranslated leader sequences that result in a transcriptional overlap of 80 bp. Interestingly, deletion of a 26-bp region containing an inverted repeat sequence resulted in the loss of expression from both the abcA and the pbpD promoters, These data prov ide evidence that abcA and pbpD are under the control of a common regu latory mechanism that may involve the transport function of the abcA g ene product.