Abstract
The regulation model of the Staphylococcus aureus pathogenicity island SaPIbov1 transfer was recently reported. The repressor protein Stl obstructs the expression of SaPI proteins Str and Xis, latter which is responsible for mobilization initiation. Upon Φ11 phage infection of S. aureus. phage dUTPase activates the SaPI transfer via Stl-dUTPase complex formation. Our aim was to predict the binding sites for the Stl repressor within the S. aureus pathogenicity island DNA sequence. We found that Stl was capable to bind to three 23-mer oligonucleotides, two of those constituting sequence segments in the stl-str, while the other corresponding to sequence segment within the str-xis intergenic region. Within these oligonucleotides, mutational analysis revealed that the predicted binding site for the Stl protein exists as a palindromic segment in both intergenic locations. The palindromes are built as 6-mer repeat sequences involved in Stl binding. The 6-mer repeats are separated by a 5 oligonucleotides long, nonspecific sequence. Future examination of the interaction between Stl and its binding sites in vivo will provide a molecular explanation for the mechanisms of gene repression and gene activation exerted simultaneously by the Stl protein in regulating transfer of the SaPIbov1 pathogenicity island in S. aureus.
Highlights
Staphylococcus aureus pathogenicity islands (SaPIs) have a major role in spreading virulence genes among bacterial populations [1], as they encode major antigens responsible for different toxinoses, such as the toxin of Toxic Shock Syndrome (TSS)
We performed Electrophoretic Mobility Shift Assay (EMSA) experiment with this oligonucleotide, and found that Stl binds to this segment (Fig 2)
In question, since even the purine-purine or pyrimidine-pyrimidine symmetry has not been preserved at that specific position. We found that these mutations led to a highly attenuated binding, equivalent to that observed with an aspecific oligonucleotide (S3 Fig Panels B and C to be compared with S4 Fig)
Summary
Staphylococcus aureus pathogenicity islands (SaPIs) have a major role in spreading virulence genes among bacterial populations [1], as they encode major antigens responsible for different toxinoses, such as the toxin of Toxic Shock Syndrome (TSS). The SaPI life cycle can be initiated and realized only in the presence of certain helper bacteriophages, which counteract the SaPI repressor (Stl) and provide the proteins necessary for SaPI packaging into infectious particles
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