The goal of the proposed research is to understand how processing and movement of messenger RNAs out of the nucleus is coordinated. Following their synthesis, mRNAs are subjected to extensive processing including capping, splicing, polyadenylation and packaging into protein-RNA particles for export out of the nucleus. An analysis of macromolecular trafficking across the nuclear envelope in the yeast Saccharomyces cerevisiae has revealed several key factors that play a role in mRNA processing and export out of the nucleus. These include: the NPL3 and HRP1 genes, which encode hnRNP proteins; HMT1, which encodes a novel protein methyltransferase and the CBP genes, which encode the major RNA cap binding proteins. The proposed experiments build on these observations and focus on three interrelated processes -binding of proteins to the 5' pre-mRNA cap, polyadenylation and export of mRNA through the nuclear pore and one enzyme - the novel arginine methyltransferase.
The Specific Aims are: 1) to determine if there are additional arginine methyltransferases in yeast and to assess the reversibility of methylation on arginine; 2) to assess how mRNA polyadenylation is affected by protein methylation; 3) to define the relationship between polyadenylation factors and mRNA movement out of the nucleus; 4) to delineate the relationship between the RNA Cap Binding Complex (CBC) and mRNA export form the nucleus; and 5) to design novel inhibitors specific for arginine methyltransferases. Many viruses have been shown to exploit the endogenous nuclear import and export machinery in order to propagate. The finding that host proteins implicated in RNA export are, for example, methylated at arginine suggested that similar modifications might occur on viral proteins crucial for export of viral RNAs and this has been shown to be the case. An understanding of the role of methylation in cellular processes could lead to the discovery of new uses for methyltransferase inhibitors or inducers in, for example, treating viral infection. It is also of interest to note that both types of arginine-methylated proteins, hnRNPs and myelin basic protein, are prominent in autoimmune diseases; systemic lupus erythmatosis and multiple sclerosis, respectively. It may be that modified arginine has distinctive recognition properties that lead to initiation or exacerbation of autoimmune diseases. An understanding of the basic recognition properties of methylated arginine may be useful in finding out why such proteins are targets in autoimmune disease.
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