Staphylococcus aureus pathogenicity islands (SaPIs) are genetic elements that are mobilized by specific helper phages. The initial step in mobilization is the derepression of the SaPI by the interaction of a phage protein with the SaPI master repressor Stl. Stl proteins are highly divergent between different SaPIs and respond to different phage-encoded derepressors. One such SaPI, SaPIbov1, is derepressed by the dUTPase (Dut) of bacteriophage 80α (Dut80α) and its phage ϕ11 homolog, Dut11. We previously showed that SaPIbov1 could also be mobilized by phage ϕNM1, even though its dut gene is not homologous with that of 80α. Here, we show that ϕNM1 dut encodes a type 2 dUTPase (DutNM1), which has an α-helical structure that is distinct from the type 1 trimeric, β-sheet structure of Dut80α. Deletion of dutNM1 abolishes the ability of ϕNM1 to mobilize SaPIbov1. Like Dut80α, DutNM1 forms a direct interaction with SaPIbov1 Stl both in vivo and in vitro, leading to inhibition of the dUTPase activity and Stl release from its target DNA. This work provides novel insights into the diverse mechanisms of genetic mobilization in S. aureus.
Keywords: genetic regulation; high-frequency transduction; horizontal gene transfer; molecular piracy; staphylococcal repressor.
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