Essential tubulin-folding protein involved in the final step of the tubulin folding pathway. Required for continuous microtubule cytoskeleton organization, mitotic division, cytokinesis, and to couple cell cycle progression to cell division in embryos and endosperms. Not essential for cell viability. Binds probably to the multimeric supercomplex, stimulating GTP hydrolysis by the bound beta-tubulin and the release of the alpha-/beta-tubulin heterodimer. Supercomplex made of cofactors A to E. Cofactors A and D function by capturing and stabilizing tubulin in a quasi-native conformation. Cofactor E binds to the cofactor D-tubulin complex; interaction with cofactor C then causes the release of tubulin polypeptides that are committed to the native state. Not associated with microtubular arrays. Ubiquitously expressed (at protein level). Present in leaves, roots, flowers, and stems. Disturbed microtubule organization. Lethal embryos that consist of one or a few grossly enlarged cells that lack microtubules but not actin filaments. Failure to localize KNOLLE in mitotic cells. Cortical microtubules-free interphase cells and mitotic nuclei missing spindles. Reduced trichome size with fewer branches. Belongs to the PILZ group of genes that disrupt, when mutated, the microtubule cytoskeleton and produce mushroom-shaped ('pilz' in German) embryos. Belongs to the TBCC family.