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β-COP, a 110kD protein associated with non-clathrin-coated vesicles and the Golgi complex, shows homology to β-adaptin
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A coat subunit of Golgi-derived non-clathrin-coated vesicles with homology to the clathrin-coated vesicle coat protein [3-adaptin T. Serafini et al. Nature 349, 215-220
[3-COP, a 11OED protein associated with non-clathrin-coated vesicles and the Golgi complex, shows homology to [3-adaptin R. Duden, G. Griffiths, R. Frank, P. Argos and T. E. Kreis Cell 64, 649-665
Brefeldin A, a drug that blocks secretion, prevents the assembly of non-clathrin-coated buds on Golgi cisternae L. Orci et al. Cell 64, 1183-1195
The latest findings on 13-COP are discussedin the review on page 14.
At first, most evidence seemed to indicate that the clathrin-coated vesicles involved in receptor-mediated endocytosis and the non-clathrincoated vesicles that transport proteins between the compartments of the Golgi complex would be as distinct in biochemistry as they are in function. This has turned out not to be the case, as the major coat proteins of both have nearly identical polypeptide molecular weights, and
the non-clathrin-coated vesicle protein, 13-COP, has significant sequence homology with 13-adaptin of clathrin-coated vesicles. These results, along with the growing body of data that also implicates a family of small GTPases in membrane transport, may presage the perception of an unexpected simplicity in the seemingly disparate events of transport through the Golgi complex, exocytosis and
endocytosis. Orci et aL, using the vesicle researcher's wonder drug brefeldin A, have now shown that the drug prevents formation of nonclathrin-coated vesicles, and induces gross morphotogical changes in the Golgi cisternae, in a cell-free system. This may provide both an explanation for the effects of the drug and a useful new tool to investigate the organization of the Golgi apparatus.
Kinesin heavy chain is essential for viability and neuromuscular functions in Drosophila, but mutants show no defects in mitosis
heavy chain (the subunit that contains the force-generating 'head' domain) has helped to establish a new paradigm for motility studies in vitro. The kinesin heavy chain, which seems to be ubiquitous in eukaryotes, has rapidly become the archetype for an extended protein superfamily, as mutant phenotypes in several experimental organisms have been traced to gene products containing a domain homologous to the 'head' of the kinesin heavy chain. This has raised the new questions of how many and which aspects of microtubulebased motility are mediated by kinesin and by the kinesin-like proteins. Sa×ton et al. have isolated Drosophila harbouring mutations in the kinesin heavy chain gene, and asked what effects these lesions produce in viva. Most disruptions of the gene are lethal in homozygotes, yet growth rate and neuromuscular functions are affected rather than embryogenesis (i.e. mitosis). The authors suggest a role for kinesin in the neuromuscular system as a motor for axonal transport. This study adds kinesin heavy chain mutants to the arsenal of biochemical and molecular tools that have provided fascinating glimpses into the workings of the kinesin family.
Pheromone-induced phosphorylation of a G protein 13subunit in S. cerevislae is associated with an adaptive response to mating pheromone
W. M. Saxton, J. Hicks, L. S. B. Goldstein and E. C. Raft Cell 64, 1093-1102 The movement of chromosomes, vesicles, and other organelles along cytoplasmic microtubules have fascinated more than one generation of cell biologists. The first inklings of how these events are accomplished, on a molecular scale, came with the discovery and purification of kinesin from squid axoplasm, and the demonstration of this protein's ATPdependent capacity to move particles along microtubules. That work, ~,ld the subsequent molecular cloning and dissection of the Drosophila melanogaster kinesin
12
G. M. Cole and S. I. Reed Cell 64, 703-716 Heterotrimeric G proteins are widely implicated in signal transduction. The G protein that mediates the response of a yeast cell to mating pheromone is unusual in that Gp, rather than G~, transmits the signal to prepare for mating. This paper shows that the GI~ subunit is rapidly phosphorylated in response to pheromone. Cells harbouring a Gp mutant which cannot be phosphorylated are competent to transmit the pheromone signal, but impaired in their ability to adapt to continuing signal in the absence of productive mating. Thus, GI~ phosphorylation represents a novel mechanism for desensitization to an ongoing stimulus, which acts in concert with known receptormediated mechanisms.
TRENDS IN CELL BIOLOGYVOL. 1 JULY1991
A coat subunit of Golgi-derived non-clathrin-coated vesicles with homology to the clathrin-coated vesicle coat protein [3-adaptin T. Serafini et al. Nature 349, 215-220
[3-COP, a 11OED protein associated with non-clathrin-coated vesicles and the Golgi complex, shows homology to [3-adaptin R. Duden, G. Griffiths, R. Frank, P. Argos and T. E. Kreis Cell 64, 649-665
Brefeldin A, a drug that blocks secretion, prevents the assembly of non-clathrin-coated buds on Golgi cisternae L. Orci et al. Cell 64, 1183-1195
The latest findings on 13-COP are discussedin the review on page 14.
At first, most evidence seemed to indicate that the clathrin-coated vesicles involved in receptor-mediated endocytosis and the non-clathrincoated vesicles that transport proteins between the compartments of the Golgi complex would be as distinct in biochemistry as they are in function. This has turned out not to be the case, as the major coat proteins of both have nearly identical polypeptide molecular weights, and
the non-clathrin-coated vesicle protein, 13-COP, has significant sequence homology with 13-adaptin of clathrin-coated vesicles. These results, along with the growing body of data that also implicates a family of small GTPases in membrane transport, may presage the perception of an unexpected simplicity in the seemingly disparate events of transport through the Golgi complex, exocytosis and
endocytosis. Orci et aL, using the vesicle researcher's wonder drug brefeldin A, have now shown that the drug prevents formation of nonclathrin-coated vesicles, and induces gross morphotogical changes in the Golgi cisternae, in a cell-free system. This may provide both an explanation for the effects of the drug and a useful new tool to investigate the organization of the Golgi apparatus.
Kinesin heavy chain is essential for viability and neuromuscular functions in Drosophila, but mutants show no defects in mitosis
heavy chain (the subunit that contains the force-generating 'head' domain) has helped to establish a new paradigm for motility studies in vitro. The kinesin heavy chain, which seems to be ubiquitous in eukaryotes, has rapidly become the archetype for an extended protein superfamily, as mutant phenotypes in several experimental organisms have been traced to gene products containing a domain homologous to the 'head' of the kinesin heavy chain. This has raised the new questions of how many and which aspects of microtubulebased motility are mediated by kinesin and by the kinesin-like proteins. Sa×ton et al. have isolated Drosophila harbouring mutations in the kinesin heavy chain gene, and asked what effects these lesions produce in viva. Most disruptions of the gene are lethal in homozygotes, yet growth rate and neuromuscular functions are affected rather than embryogenesis (i.e. mitosis). The authors suggest a role for kinesin in the neuromuscular system as a motor for axonal transport. This study adds kinesin heavy chain mutants to the arsenal of biochemical and molecular tools that have provided fascinating glimpses into the workings of the kinesin family.
Pheromone-induced phosphorylation of a G protein 13subunit in S. cerevislae is associated with an adaptive response to mating pheromone
W. M. Saxton, J. Hicks, L. S. B. Goldstein and E. C. Raft Cell 64, 1093-1102 The movement of chromosomes, vesicles, and other organelles along cytoplasmic microtubules have fascinated more than one generation of cell biologists. The first inklings of how these events are accomplished, on a molecular scale, came with the discovery and purification of kinesin from squid axoplasm, and the demonstration of this protein's ATPdependent capacity to move particles along microtubules. That work, ~,ld the subsequent molecular cloning and dissection of the Drosophila melanogaster kinesin
12
G. M. Cole and S. I. Reed Cell 64, 703-716 Heterotrimeric G proteins are widely implicated in signal transduction. The G protein that mediates the response of a yeast cell to mating pheromone is unusual in that Gp, rather than G~, transmits the signal to prepare for mating. This paper shows that the GI~ subunit is rapidly phosphorylated in response to pheromone. Cells harbouring a Gp mutant which cannot be phosphorylated are competent to transmit the pheromone signal, but impaired in their ability to adapt to continuing signal in the absence of productive mating. Thus, GI~ phosphorylation represents a novel mechanism for desensitization to an ongoing stimulus, which acts in concert with known receptormediated mechanisms.
TRENDS IN CELL BIOLOGYVOL. 1 JULY1991