Derepression of SaPIbov1 Is Independent of φNM1 Type 2 dUTPase Activity and Is Inhibited by dUTP and dUMP

Staphylococcus aureus is an opportunistic human pathogen able to transfer virulence genes to other cells through the mobilization of S. aureus pathogenicity islands (SaPIs). SaPIs are derepressed and packaged into phage-like transducing particles by helper phages like 80 alpha or phi NM1. Phages 80 alpha and phi NM1 encode structurally distinct dUTPases, Dut(80 alpha) (type 1) and Dut(NM1) (type 2). Both dUTPases can interact with the SaPIbov1 Stl master repressor, leading to derepression and mobilization. That two structurally distinct dUTPases bind the same repressor led us to speculate that dUTPase activity may be important to the derepression process. In type 1 dUTPases, Stl binding is inhibited by dUTP. The purpose of this study was to assess the involvement of dUTP binding and dUTPase activity in derepression by Dut(NM1). Dut(NM1) activity mutants were created and tested for dUTPase activity using a novel NMR-based assay. We found that all Dut(NM1) null activity mutants interacted with the SaPIbov1 Stl C-terminal domain, formed Dut(NM1)-Stl heterodimers, and caused the release of the P-str promoter. However, promoter release was inhibited in the presence of dUTP or dUMP. We tested phi NM1 mutant phages that had null enzyme activity and found that they could still mobilize SaPIbov1. These results show that only the apo form of Dut(NM1) is active in Stl derepression and that dUTPase activity is not necessary for the mobilization of SaPIbov1 by Dut(NM1). (C) 2017 Elsevier Ltd. All rights reserved.