SaPIs are mobilized through derepression by phage proteins.
SaPIbov1 is derepressed by phage ϕNM1 Dut, a type 2 α-helical dUTPase (DutNM1).
DutNM1 interacts with the SaPIbov1 Stl repressor, releasing it from its DNA target.
Interaction with Stl leads to inhibition of the dUTPase activity of DutNM1.
This work suggests a novel mechanism for the derepression that leads to SaPI mobilization.