Microtubules are polymers of tubulin, a dimer of two 55kDa subunits, designated alpha and beta [<cite idref="PUB00000039"/>, <cite idref="PUB00000978"/>]. Within the microtubule lattice, alpha-betaheterodimers associate in a head-to-tail fashion, giving rise to microtubule polarity. Fluorescent labelling studies have suggested that tubulin isoriented in microtubules with beta-tubulin toward the plus end [<cite idref="PUB00006112"/>]. For maximal rate and extent of polymerisation into microtubules, tubulin requires GTP. Two molecules of GTP are bound at different sites, termed N and E. At the E (Exchangeable) site, GTP is hydrolysed during incorporationinto the microtubule. Close to the E site is an invariant region rich in glycine residues, which is found in both chains and is thought to controlaccess of the nucleotide to its binding site [<cite idref="PUB00002443"/>]. <p>Most species, excepting simple eukaryotes, express a variety of closely related alpha- and beta-isotypes. A third family member, gamma tubulin, hasalso been identified in a number of species [<cite idref="PUB00000721"/>].British type familial amyloidosis is an autosomal dominant disease characterised by progressive dementia, spastic paralysis and ataxia. Amyloid deposits from the brain tissue of an individual who died with this disease have been characterised. Trypsin digestion and subsequent N-terminalsequence analysis yielded a number of short sequences, all of which aretryptic fragments of the C-termini of human alpha- and beta-tubulin. Consistent with the definition of amyloid, synthetic peptides based on the sequences of these fragments formed fibrils <i>in vitro</i>, suggesting that theC-termini of both alpha- and beta-tubulin are closely associated with theamyloid deposits of this type of amyloidosis [<cite idref="PUB00006129"/>]. The amino acid sequences encoded by beta tubulin genes have revealed a high level of overall similarity, but significant divergence between theirC-termini [<cite idref="PUB00006090"/>]. The pattern of expression of the beta-tubulin genes has been studied in several different human cell lines and has revealed varying levels of and differential expression in different cell lines. Itappears that distinct human beta-tubulin isotypes are encoded by geneswhose exon size and number has been conserved evolutionarily, but whose pattern of expression may be regulated either co-ordinately or uniquely [<cite idref="PUB00006090"/>].</p> Beta tubulin