| Summary: | <p>Abstract</p> <p>Background</p> <p><it>Staphylococcus aureus </it>immunodominant surface antigen B (IsaB) elicits an immune response during septicemia and is generally classified as a virulence factor, but its biological function remains completely undefined. In an attempt to identify staphylococcal RNA-binding proteins, we designed an RNA Affinity Chromatography assay and subsequently isolated IsaB.</p> <p>Results</p> <p>Western analysis indicated that IsaB was both secreted and cell-surface associated. Gel Shift analysis confirmed the RNA binding activity but revealed that IsaB bound to any nucleic acid without sequence specificity. IsaB exhibited the highest affinity for double-stranded DNA followed by single-stranded DNA and RNA. Because extracellular DNA has been shown to play a role in biofilm formation, we investigated the biofilm-forming capacity of an isogenic <it>isaB </it>deletion mutant but we found that IsaB did not contribute to biofilm formation under any conditions tested.</p> <p>Conclusion</p> <p>IsaB is an extracellular nucleic acid binding protein, with little to no sequence specificity, but its role in virulence remains unclear.</p>
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