TUBB (beta tubulin class I) is protein that forms a dimer with alpha tubulin to act as a major constituent of microtubules. It binds two moles of GTP, one at an exchangeable site on the beta chain (TUBB) and one at a non-exchangeable site on the alpha chain. Inherited TUBB mutations lead to development brain defects including cortical dysplasia, while somatic mutations are correlated with drug resistance in cancer. In immunohistochemistry, TUBB has variable degrees of cytoplasmic positivity in all tissues. References: Hum Genet. 1994 Jan;93(1):42-6, PMID: 8270253; Biochem Biophys Res Commun. 2016 Aug 5;476(4):273-279, PMID: 27233604; J Biomol Struct Dyn. 2015;33(12):2530-40, PMID: 26081685; Mol Cancer Ther. 2011 Aug;10(8):1419-29, PMID: 21653684