The export of mRNA from its site of biogenesis in the nucleus to sites of translation in the cytoplasm is a key step of the gene expression pathway. During export, the mRNP (mRNA plus bound proteins) passes through the central channel of the nuclear pore complex (NPC). S. cerevisiae Dbp5, a DEAD box protein and important conserved mediator of mRNA export, interacts with two proteins located on the cytoplasmic face of the yeast NPC, the cytoplasmic filament nucleoporin, Nup159, and Gle1. Gle1 and inositol hexakisphosphate (IP6), activate the RNA-dependent ATPase of Dbp5. This generates Dbp5-ADP, which can remove bound proteins from mRNP in vitro. Dbp5 is hypothesized to do this in vivo, altering the exported mRNP so that export is irreversible. Understanding Dbp5's interactions with proteins and mRNPs at the NPC and defining its cycle is key to our understanding of gene expression.
Three specific aims are proposed for the next project period. (1) Aim 1 is to delineate steps of the Dbp5 cycle. Using a combination of genetic, biochemical and imaging approaches, the interactions of Dbp5 with both Nup159 and Gle1 will be quantitated and the dynamics of these interactions will be measured by using FRAP. The hypothesis that binding to Nup159 is the first step in the Dbp5 cycle and facilitates its interaction with its activator, Gle1, will be tested. These studies will also address whether Dbp5 must cycle through the nucleus to perform its role in mRNA export. Dominant negative (DN) mutants will be characterized and used to determine which functions must be present and absent for a mutant to be DN. Potential new binding partners of Dbp5 will be identified by using mass spectrometry. The functions of the N- and C-terminal regions of Dbp5 will be investigated. (2) Aim 2 is to investigate Gle1's interaction with NPCs. The hypothesis that Gle1 binds to NPCs not only through Nup42 but also through an additional nup will be explored and the predicted binding partner identified. The dynamics of Gle1's interaction with NPCs will be investigated and a set of new ts mutants of Gle1 will be characterized in an attempt to identify a Gle1 that produces a stable protein and whose mutation affects Gle1's function in mRNA export but not protein synthesis. (3) Aim 3 is to define the role of Nup159 in mRNA export. The N-terminus of Nup159 is a seven-bladed betapropeller and Dbp5 binds to blades 1, 6, and 7. The hypothesis that Nup159's N terminus provides a binding site for an additional protein that participates in mRNA export will be investigated using genetics, biochemistry, and mass spectrometry. Nup159 fused to a photoconvertible GFP will be employed to explore the dynamics of Nup159 and cytoplasmic filament association with NPCs.
The transport of messenger RNA from its site of synthesis in the nucleus to its sites of translation in the cytoplasm is a fundamental step in gene expression. Understanding how mRNA export works is essential for a complete understanding of cellular structure and function. Many viruses exploit Mrna transport, either to prevent export of host mRNAs or to facilitate export of their own mRNAs or both. In addition, mutations affecting key mRNA export factors have been linked to human diseases include cancer, heart disease, and neurological disease.
|Hodge, Christine A; Tran, Elizabeth J; Noble, Kristen N et al. (2011) The Dbp5 cycle at the nuclear pore complex during mRNA export I: dbp5 mutants with defects in RNA binding and ATP hydrolysis define key steps for Nup159 and Gle1. Genes Dev 25:1052-64|
|Noble, Kristen N; Tran, Elizabeth J; Alcázar-Román, Abel R et al. (2011) The Dbp5 cycle at the nuclear pore complex during mRNA export II: nucleotide cycling and mRNP remodeling by Dbp5 are controlled by Nup159 and Gle1. Genes Dev 25:1065-77|
|Hodge, Christine A; Choudhary, Vineet; Wolyniak, Michael J et al. (2010) Integral membrane proteins Brr6 and Apq12 link assembly of the nuclear pore complex to lipid homeostasis in the endoplasmic reticulum. J Cell Sci 123:141-51|
|Estruch, Francisco; Peiro-Chova, Lorena; Gomez-Navarro, Natalia et al. (2009) A genetic screen in Saccharomyces cerevisiae identifies new genes that interact with mex67-5, a temperature-sensitive allele of the gene encoding the mRNA export receptor. Mol Genet Genomics 281:125-34|
|Scarcelli, John J; Viggiano, Susan; Hodge, Christine A et al. (2008) Synthetic genetic array analysis in Saccharomyces cerevisiae provides evidence for an interaction between RAT8/DBP5 and genes encoding P-body components. Genetics 179:1945-55|
|Scarcelli, John J; Hodge, Christine A; Cole, Charles N (2007) The yeast integral membrane protein Apq12 potentially links membrane dynamics to assembly of nuclear pore complexes. J Cell Biol 178:799-812|
|Rollenhagen, Christiane; Hodge, Christine A; Cole, Charles N (2007) Following temperature stress, export of heat shock mRNA occurs efficiently in cells with mutations in genes normally important for mRNA export. Eukaryot Cell 6:505-13|
|Cole, Charles N; Scarcelli, John J (2006) Transport of messenger RNA from the nucleus to the cytoplasm. Curr Opin Cell Biol 18:299-306|
|Dunn, Ewan F; Hammell, Christopher M; Hodge, Christine A et al. (2005) Yeast poly(A)-binding protein, Pab1, and PAN, a poly(A) nuclease complex recruited by Pab1, connect mRNA biogenesis to export. Genes Dev 19:90-103|
|Rollenhagen, Christiane; Hodge, Christine A; Cole, Charles N (2004) The nuclear pore complex and the DEAD box protein Rat8p/Dbp5p have nonessential features which appear to facilitate mRNA export following heat shock. Mol Cell Biol 24:4869-79|
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