Structural domains comprising this superfamily share the structure of the plasmid SOS inhibition protein (PsiB), which is encoded by the F plasmid and is involved in the binding and sequestering RecA to prevent filament formation. PsiB acts by preventing RecA from binding to DNA by binding free RecA. RecA is a central protein in DNA recombination and translesion DNA synthesis but it also mediates SOS induction through formation of RecA protein filaments on ssDNA. There are many characterized RecA modulator proteins, but PsiB is unique in using sequestration as its inhibitory mechanism. Structural analysis has shown that the structure of PsiB is surprisingly similar to CapZ, a eukaryotic actin filament capping protein PMID:20659894.