Stathmin/Op18 is a 21 - 23 kD member of the Stathmin family. This protein is localized in the cytoplasm and becomes nuclear during the S/G2 phase of the cell cycle. Stathmin/Op18 acts as a microtubule destabilizer in mitotic spindle regulation and sequesters tubulin dimers into assembly-incompetent complexes. This protein participates as an intracellular relay integrating regulatory signals of the cellular environment and has been shown to be involved in megakaryocyte polyploidization. Stathmin/Op18 can be phosphorylated in response to heat; Ser62 phosphorylation reduces tubulin binding ability. This protein can also be modified by acetylation. Stathmin/Op18 has been shown to interact with tubulin, KIST, CaM kinase II and IV, Cdc2, MAPK, and Cdk1. The Poly6202 antibody recognizes human phosphorylated stathmin/Op18 (Ser16) and has been shown to be useful for Western blotting.