Plays an important role in the organization of the cytoskeleton. Binds to and sequesters actin monomers (G actin) and therefore inhibits actin polymerization. Potent inhibitor of bone marrow derived stem cell differentiation (By similarity). Acts by inhibits the entry of hematopoietic pluripotent stem cells into the S-phase (By similarity). Identified in a complex composed of ACTA1, COBL, GSN AND TMSB4X (By similarity). Interacts with SERPINB1 (By similarity). Originally found in thymus but it is widely distributed in many tissues. AcSDKP is inactivated by ACE, which removes the dipeptide Lys-Pro from its C-terminus. Belongs to the thymosin beta family.