Regulatory subunit of serine/threonine-protein phosphatase 4 (PP4). May regulate the activity of PPP4C at centrosomal microtubule organizing centers (By similarity). Serine/threonine-protein phosphatase 4 (PP4) occurs in different assemblies of the catalytic and one or more regulatory subunits. Component of the PP4 complex PPP4C-PPP4R2-PPP4R3B. In interphase localized in the cytoplasm and (with higher levels) the nucleus. During metaphase located in pericentriolar regions. Belongs to the SMEK family.