β-transducin (G-β) is one of the three subunits (α, β, and γ)
of the guanine nucleotide-binding proteins (G proteins) which act as
intermediaries in the transduction of signals generated by transmembrane
receptors . The α subunit binds to and hydrolyzes GTP; the functions of
the β and γ subunits are less clear but they seem to be required for
the replacement of GDP by GTP as well as for membrane anchoring and
In higher eukaryotes G-β exists as a small multigene family of highly
conserved proteins of about 340 amino acid residues. Structurally G-β
consists of eight tandem repeats of about 40 residues, each containing a
central Trp-Asp motif (this type of repeat is sometimes called a WD-40
repeat). Such a repetitive segment has been shown [2,3,4,5] to exist in a
number of other proteins listed below:
Yeast STE4, a component of the pheromone response pathway. STE4 is a G-β
like protein that associates with GPA1 (G-α) and STE18 (G-γ).
Yeast MSI1, a negative regulator of RAS-mediated cAMP synthesis. MSI1 is
most probably also a G-β protein.
Human and chicken protein 12.3. The function of this protein is not known,
but on the basis of its similarity to G-β proteins, it may also function
in signal transduction.
Chlamydomonas reinhardtii gblp. This protein is most probably the homolog
of vertebrate protein 12.3.
Human LIS1, a neuronal protein involved in type-1 lissencephaly.
Mammalian coatomer β' subunit (β'-COP), a component of a cytosolic
protein complex that reversibly associates with Golgi membranes to form
vesicles that mediate biosynthetic protein transport.
Yeast CDC4, essential for initiation of DNA replication and separation of
the spindle pole bodies to form the poles of the mitotic spindle.
Yeast CDC20, a protein required for two microtubule-dependent processes:
nuclear movements prior to anaphase and chromosome separation.
Yeast MAK11, essential for cell growth and for the replication of M1
Yeast PRP4, a component of the U4/U6 small nuclear ribonucleoprotein with
a probable role in mRNA splicing.
Yeast PWP1, a protein of unknown function.
Yeast SKI8, a protein essential for controlling the propagation of double-
Yeast SOF1, a protein required for ribosomal RNA processing which
associates with U3 small nucleolar RNA.
Yeast TUP1 (also known as AER2 or SFL2 or CYC9), a protein which has been
implicated in dTMP uptake, catabolite repression, mating sterility, and
many other phenotypes.
Yeast YCR57c, an ORF of unknown function from chromosome III.
Yeast YCR72c, an ORF of unknown function from chromosome III.
Slime mold coronin, an actin-binding protein.
Slime mold AAC3, a developmentally regulated protein of unknown function.
Drosophila protein Groucho (formerly known as E(spl); 'enhancer of split'),
a protein involved in neurogenesis and that seems to interact with the
Notch and Delta proteins.
Drosophila TAF-II-80, a protein that is tightly associated with TFIID.
The number of repeats in the above proteins varies between 5 (PRP4, TUP1, and
Groucho) and 8 (G-β, STE4, MSI1, AAC3, CDC4, PWP1, etc.). In G-β and G-β like proteins, the repeats span the entire length of the sequence, while
in other proteins, they make up the N-terminal, the central or the C-terminal
A signature pattern can be developed from the central core of the domain
(positions 9 to 23).
Two profiles were developed for this module, the first one picks up WD repeats
while the second profile is 'circular' and will thus detect a region
containing adjacent WD repeats.
December 2004 / Pattern and text revised.
PROSITE methods (with tools and information) covered by this documentation:
G proteins: transducers of receptor-generated signals.
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