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Prion discovery gives clue to control of mass gene expression
March 16, 2009The discovery in common brewer's yeast of a new, infectious, misfolded protein -- or prion -- by University of Illinois at Chicago molecular biologists raises new questions about the roles played by these curious molecules, often associated with degenerative brain diseases like "mad cow" and its human counterpart, Creutzfeldt-Jakob.
Susan Liebman, distinguished university professor of biological sciences, and postdoctoral research associate Basant Patel propagated the new prion from a normal yeast protein called Cyc8. They note that like the Cyc8 protein, the prion of Cyc8 can affect the expression of a large number of yeast genes.
"We know this prion turns on the expression of genes but we don't know if the prion forms naturally," said Liebman. "If it were to form, it would have this effect. But whether it happens out in the wild all the time, we don't know."
Liebman and her coworkers discovered that Cyc8 was a prion candidate using a genetic screen that looks for proteins that when overproduced can spur formation of new prions. To date, scientists have discovered only seven prions, six of which are only in fungi, including yeast. The latest two discovered, Cyc8 and another, identified as Swi1, came from genes screened in Liebman's lab. The Cyc8 prion was characterized by the UIC scientists, while the Swi1 prion was found by Northwestern University researchers.
The normal Cyc8 protein shuts down expression of more than 300 genes in yeast, says Patel, including some genes that are involved in stress tolerance.
"Once Cyc8 is converted to a prion, it loses that function," he said. "This might provide some advantages under stressful conditions. Since the protein represses more than 300 genes, it's possible the prion form can activate the genes on a mass level." If an organism wanted to activate all the genes in a cell that the protein repressed, he said, "converting the protein into a prion would be an easy way to do it."
Patel and others in Liebman's lab are testing the protein to see if this molecular mechanism does in fact take place naturally. They're also studying the interaction of prions to determine if pre-existing prions facilitate or destabilize new prions.
Whether the actions of prions in yeast are analogous to mammalian models is not yet fully known, but the possibility certainly is on the minds of Liebman and her associates.
"There could be prions in humans that are not causing disease but have important effects on the cell or organism," said Liebman. "They may even be related to the ones we find in yeast. The more prions we learn about and study, the more information we learn from them -- how they arrive, what proteins are needed to maintain them. As we study other models, we have a better idea."
University of Illinois at Chicago
Liebman and her coworkers discovered that Cyc8 was a prion candidate using a genetic screen that looks for proteins that when overproduced can spur formation of new prions. To date, scientists have discovered only seven prions, six of which are only in fungi, including yeast. The latest two discovered, Cyc8 and another, identified as Swi1, came from genes screened in Liebman's lab. The Cyc8 prion was characterized by the UIC scientists, while the Swi1 prion was found by Northwestern University researchers.
The normal Cyc8 protein shuts down expression of more than 300 genes in yeast, says Patel, including some genes that are involved in stress tolerance.
"Once Cyc8 is converted to a prion, it loses that function," he said. "This might provide some advantages under stressful conditions. Since the protein represses more than 300 genes, it's possible the prion form can activate the genes on a mass level." If an organism wanted to activate all the genes in a cell that the protein repressed, he said, "converting the protein into a prion would be an easy way to do it."
Patel and others in Liebman's lab are testing the protein to see if this molecular mechanism does in fact take place naturally. They're also studying the interaction of prions to determine if pre-existing prions facilitate or destabilize new prions.
Whether the actions of prions in yeast are analogous to mammalian models is not yet fully known, but the possibility certainly is on the minds of Liebman and her associates.
"There could be prions in humans that are not causing disease but have important effects on the cell or organism," said Liebman. "They may even be related to the ones we find in yeast. The more prions we learn about and study, the more information we learn from them -- how they arrive, what proteins are needed to maintain them. As we study other models, we have a better idea."
University of Illinois at Chicago
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Prion study reveals first direct information about the protein's molecular structure
A collaboration between scientists at Vanderbilt University and the University of California, San Francisco has led to the first direct information about the molecular structure of prions.
U of T led research team uncovers evolutionary origins of prion disease gene
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Species barrier may protect macaques from chronic wasting disease
Data from an ongoing multi-year study suggest that people who consume deer and elk with chronic wasting disease (CWD) may be protected from infection by an inability of the CWD infectious agent to spread to people.
A Penny for Your Prions
North Carolina State University researchers have discovered a link between copper and the normal functioning of prion proteins, which are associated with transmissible spongiform encephalopathy diseases such as Cruetzfeldt-Jakob in humans or "mad cow" disease in cattle.
Scripps Florida scientists devise accelerated method to determine infectious prion strainsScripps Florida scientists devise accelerated method to determine infectious prion strains
Current tests to identify specific strains of infectious prions, which cause a range of transmissible diseases (such as mad cow) in animals and humans, can take anywhere from six months to a year to yield results - a time-lag that may put human populations at risk.
Prevalence of variant CJD agent in Britain remains uncertain
First results from a large tissue survey in Britain of the agent that causes variant Creutzfeldt-Jakob disease (vCJD) are unable so far to establish that the prevalence is lower than that given by previous estimates, concludes a study published on bmj.com today.
Redefining what it means to be a prion
Whitehead Institute researchers have quintupled the number of identifiable prion proteins in yeast and have further clarified the role prions play in the inheritance of both beneficial and detrimental traits.
Iron is involved in prion disease-associated neuronal demise
Imbalance of iron homeostasis is a common feature of prion disease-affected human, mouse, and hamster brains, according to a new study by Dr. Neena Singh and colleagues at Case Western Reserve University School of Medicine, alongside collaborators from Creighton University.
Antibody key to treating variant CJD, scientists find
Scientists at the University of Liverpool have determined the atomic structure of the 'binding' between a brain protein and an antibody that could be key to treating patients with diseases such as variant CJD.
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