| Literature References | 1. CLEVELAND, D.W. AND SULLIVAN, K.F.
Molecular biology and genetics of tubulin.
ANNU.REV.BIOCHEMISTRY 54 331-365 (1985).
2. JOSHI, H.C. AND CLEVELAND, D.W.
Diversity among tubulin subunits: toward what functional end?
CELL MOTIL.CYTOSKELETON 16 159-163 (1990).
3. MITCHISON, T.J.
Localization of an exchangeable GTP binding site at the plus end of
microtubules.
SCIENCE 261 1044-1047 (1993).
4. HESSE, J., THIERAUF, M. AND PONSTINGL, H.
Tubulin sequence region beta 155-174 is involved in binding exchangeable
guanosine triphosphate.
J.BIOL.CHEM. 262 15472-15475 (1987).
5. JOSHI, H.C.
Gamma-tubulin: the hub of cellular microtubule assemblies.
BIOESSAYS 15 637-643 (1993).
6. ZHENG, Y., JUNG, M.K. AND OAKLEY, B.R.
Gamma-tubulin is present in Drosophila melanogaster and Homo sapiens and is
associated with the centrosome.
CELL 65 817-823 (1991).
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| Documentation | Microtubules are polymers of tubulin, a dimer of two 55kDa subunits,
designated alpha and beta [1,2]. Within the microtubule lattice, alpha-beta
heterodimers associate in a head-to-tail fashion, giving rise to microtubule
polarity. Fluorescent labelling studies have suggested that tubulin is
oriented in microtubules with beta-tubulin toward the plus end [3].
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 incorporation
into 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 control
access of the nucleotide to its binding site [4].
Most species, excepting simple eukaryotes, express a variety of closely-
related alpha- and beta-isotypes. A third family member, gamma-tubulin, has
also been identified in a number of species [5,6].
Gamma-tubulins constitute a ubiquitous and highly-conserved subfamily of
the tubulin family. The protein is found at microtubule-organising centres,
such as the spindle poles or the centrosome. It remains associated with the
centrosome when microtubules are depolymerised, suggesting that it is
an integral component that might play a role in minus-end nucleation of
microtubule assembly [5,6].
GAMMATUBULIN is an 8-element fingerprint that provides a signature for gamma-
tubulins. The fingerprint was derived from an initial alignment of 15
sequences. The motifs were drawn from conserved regions spanning virtually
the full alignment length, focusing on those sections that characterise the
gamma-tubulins but distinguish them from the rest of the tubulin family.
Two iterations on SPTR37_10f were required to reach convergence, at which
point a true set comprising 32 sequences was identified. Several partial
matches were also found, most of which are gamma-tubulins that fail to make
significant matches with one or more motifs, and two are beta-tubulins that
match two motifs.
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