Tubulin family members are globular proteins important in the assembly of microtubules. Microtubules are structural components that play important roles in mitosis, cytokinesis and vesicle transport. TPPP (Tubulin polymerization-promoting protein), also known as p24 and p25, is a widely expressed 219 amino acid protein found in the perinuclear region of the cytoplasm. TPPP may form dimers and functions in polymerizing tubulin into double-walled tubules, polymorphic aggregates, or stabilized blocks. TPPP overexpression prevents formation of the mitotic spindle assembly and breakdown of the nuclear envelope. TPPP is phosphorylated by TPK II and is encoded by a gene that maps to human chromosome 5, which contains 181 million base pairs and comprises nearly 6% of the human genome.