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© The Rockefeller University Press,
0021-9525/1999//857 $5.00
The Journal of Cell Biology, Volume 147, Number 4,
, 1999 857-868
Original Article |
Human 76p
: A New Member of the
-Tubulin–Associated Protein Family
b Service de Biochimie des Protéines, Sanofi Recherche, Labège Innopole, 31676 Labège cedex, France
IPBS-CNRS, 205 route de Narbonne, 31400 Toulouse, France.05-61-1759-9305-61-1755-17
wright{at}ipbs.fr
The role of the centrosomes in microtubule nucleation remains largely unknown at the molecular level.
-Tubulin and the two associated proteins h103p (hGCP2) and h104p (hGCP3) are essential. These proteins are also present in soluble complexes containing additional polypeptides. Partial sequencing of a 76- kD polypeptide band from these complexes allowed the isolation of a cDNA encoding for a new protein (h76p = hGCP4) expressed ubiquitously in mammalian tissues. Orthologues of h76p have been characterized in Drosophila and in the higher plant Medicago. Several pieces of evidence indicate that h76p is involved in microtubule nucleation. (1) h76p is localized at the centrosome as demonstrated by immunofluorescence. (2) h76p and -tubulin are associated in the -tubulin complexes. (3) -tubulin complexes containing h76p bind to microtubules. (4) h76p is recruited to the spindle poles and to Xenopus sperm basal bodies. (5) h76p is necessary for aster nucleation by sperm basal bodies and recombinant h76p partially replaces endogenous 76p in oocyte extracts. Surprisingly, h76p shares partial sequence identity with human centrosomal proteins h103p and h104p, suggesting a common protein core. Hence, human -tubulin appears associated with at least three evolutionary related centrosomal proteins, raising new questions about their functions at the molecular level.
Key Words: -tubulin • centrosome • microtubule • cytoskeleton • nucleation
© 1999 The Rockefeller University Press
F. Fava and B. Raynaud-Messina contributed equally to this work.Abbreviations used in this paper: DAPI, 4',6-diamidino-2-phenylindole; EST, expressed sequence tag; MTOC, microtubule organizing center; SPB, spindle pole body; TuRC,
-tubulin ring complex. Protein nomenclature. Three names have been already given to the animal orthologues of Saccharomyces Spc97p and Spc98p ( Martin et al. 1998; Murphy et al. 1998; Tassin et al. 1998; Oegema et al. 1999). (a) The Spc97p orthologues, named hGCP2 in human (human
-tubulin complex protein 2) and Dgrip84 in Drosophila (Drosophila ring protein 84), are named here h103p and d84p, respectively. (b) The Spc98p orthologues, named hGCP3 and HsSpc98 (human Spc98) in human, Xgrip109 in Xenopus (Xenopus ring protein 109), and Dgrip91 in Drosophila (Drosophila ring complex protein 91), are named here h104p, x109p, and d91p, respectively. In the absence of the 76p orthologue in Saccharomyces, the different orthologues of human 76p (hGCP4 or Hgrip76 according to previous nomenclature) were referred to as h76p, x76p, d75p, and m85p for human, Xenopus, Drosophila, and Medicago, respectively.
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