of the Golgi cytoskeleton by G-proteins.
family of GTPase proteins (Martinez
& Goud, 1998) are known to control membrane traffic
mediated through guanine-nucleotide exchange factors (GEFs) (Stow &
Heimann 1998; Ullrich
et al, 1994).
|Assembly of the Golgi
The Golgi apparatus disassembles at
mitosis and reassembles afterwards. This offers an
opportunity to study the natural assembly process.
Phosphorylation is an important key and is as one may expect, orchestrated
by many of the same kinases that direct many of the other steps
in mitosis such as spindle pole formation, nuclear
membrane breakdown and cytokinesis.
The distinctive shape of the Golgi as a series of plate-like
structures is due to proteins whose function it is to bridge the
gap between the stacks and to lock them together. One such
protein has been identified from Golgi membrane is called
"GRASP65" (Golgi Re-Assembly Stacking Protein that is
65 kDa in size (Barr et al,
1997). GRASP65 interacts with
another protein GM130. GRASP65 is a myristoylated
peripheral membrane protein and must bind to yet another partner
to explain its tropism to Golgi membranes. GM130 is
unlikely to do this as it has no detectable membrane-binding
attributes (membrane spanning domains or fatty acid
modification). However, GM130 is known to bind to p115, a
protein known to be involved in vesicle docking (Sapperstein
et al, 1996) so this may
well be the Gogli specific targeting mechanism. GRASP65 is
essential for Golgi stacking and is phosphorylated at mitosis
(as is GM130), by mitotic kinase, this phosphorylation inhibits
its interaction with p115 through GM130.
Another Golgi-specific complex is
formed by golgin-245/p230 and golgin-97. Each of these
proteins contains a so called GRIP domain which recruits
coiled-coil proteins to the Golgi (Munro
& Nichols, 1999).
|The Identity of Golgi
It is clear that the membranous
structures that form the Golgi apparatus have a constellation of
ABPs and other proteins but what makes a Golgi membrane uniquely
Golgi in the first place? The Golgi is a specialized extension
of the endoplasmic reticulum and trafficking from the two system
Barr, F. A.,
Puype, M., Vandekerckhove, J. & Warren, G. (1997) GRASP65, a protein
involved in the stacking of Golgi cisternae, Cell. 91, 253-262.
& Goud, B. (1998). "Rab proteins." BBA 1404,
Munro, S. &
Nichols, B. J. (1999) The GRIP domain - a novel Golgi-targeting domain
found in several coiled-coil proteins, Current Biol. 9, 377-380.
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Stow, J. L. & Heimann,
K. (1998). “Vesicle budding on Golgi membranes: regulation by G
proteins and myosin motors.” Biochim.Biophys.Acta.
Horiuchi, H., Bucci, C. & Zerial, M. (1994) Membrane assocation of
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