The B regulatory subunit might modulate substrate selectivity and catalytic activity, and also might direct the localization of the catalytic enzyme to a particular subcellular compartment. PP2A consists of a trimeric holoenzyme, composed of a 37 kDa catalytic subunit (C subunit) and a 65 kDa constant regulatory subunit (A subunit), that associates with a variety of regulatory subunits (B subunit) such as phr2AB (B55) and psrA (B56 homolog). The trimer may partially dissociates into a core 'AC' dimer equally active compared to the trimer (By similarity). Belongs to the phosphatase 2A regulatory subunit B family.