– Tubulin Beta-4A Chain (TUBB4A) is a cytoplasmic peptide containing 444 amino acids. TUBB4A is a member of the Tubulin family. Tubulin is the major constituent of microtubules. Tubulin is a dimer composed of one alpha and one beta tubulin molecule; there are many forms of beta tubulins, Beta II and Beta IV Tubulin are ubiquitously expressed. Beta-III Tubulin, also known as Tubulin Beta-4, is regarded as a neuron-specific marker. It binds two moles of GTP, one at an exchangeable site on the beta chain and one at a non-exchangeable site on the alpha-chain.