PROSITE documentation PDOC00199
Tubulin subunits alpha, beta, and gamma signature


Tubulins [1,2], the major constituent of microtubules are dimeric proteins which consist of two closely related subunits (α and β). Tubulin binds two molecules of GTP at two different sites (N and E). At the E (Exchangeable) site, GTP is hydrolyzed during incorporation into the microtubule. Near the E site is an invariant region rich in glycines which is found in both chains and which is now [3] said to control the access of the nucleotide to its binding site. We developed a signature pattern from this region.

With the exception of the simple eukaryotes, most species express a variety of closely related α and β isotypes.

In most species there is a third member of the tubulin family: γ tubulin. γ tubulin is found at microtubule organizing centers (MTOC) such as the spindle poles or the centrosome, suggesting that it is involved in the minus-end nucleation of microtubule assembly [4].


The first residue in the pattern is Gly in all α and β tubulins, and is Ala or Ser in γ-tubulin.


This pattern is almost identical to the GTP-binding site of the bacterial protein ftsZ (see <PDOC00873>) whose role in prokaryotes is probably similar to that of tubulins.

Last update:

November 1995 / Text revised.


Technical section

PROSITE method (with tools and information) covered by this documentation:

TUBULIN, PS00227; Tubulin subunits alpha, beta, and gamma signature  (PATTERN)


1AuthorsCleveland D.W. Sullivan K.F.
TitleMolecular biology and genetics of tubulin.
SourceAnnu. Rev. Biochem. 54:331-365(1985).
PubMed ID3896122

2AuthorsJoshi H.C. Cleveland D.W.
TitleDiversity among tubulin subunits: toward what functional end?
SourceCell Motil. Cytoskeleton 16:159-163(1990).
PubMed ID2194680

3AuthorsHesse J. Thierauf M. Ponstingl H.
TitleTubulin sequence region beta 155-174 is involved in binding exchangeable guanosine triphosphate.
SourceJ. Biol. Chem. 262:15472-15475(1987).
PubMed ID3680207

4AuthorsJoshi H.C.
TitleGamma-tubulin: the hub of cellular microtubule assemblies.
SourceBioEssays 15:637-643(1993).
PubMed ID8274140

PROSITE is copyrighted by the SIB Swiss Institute of Bioinformatics and distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives (CC BY-NC-ND 4.0) License, see prosite_license.html.


View entry in original PROSITE document format
View entry in raw text format (no links)