Project Summary RNA-RNA and RNA-protein interactions lie at the heart of essential steps of the eukaryotic gene expression pathway. Defects in these interactions due to inherited mutations can result in age- dependent degeneration of the retina, motor neurons, and other neural tissues. The proposed studies will result in a better understanding of RNA-based mechanisms of gene expression in both the normal and disease states. In the next five years we will pursue three main goals, using the yeast Saccharomyces cerevisiae as a facile model system. First, we will examine the molecular mechanism of activation of the spliceosome for the first catalytic step of pre-mRNA splicing. This process requires allosteric signal transmission through RNA and protein over distances of 100 angstroms or more and results in large-scale remodeling of the spliceosome to allow progression of the splicing cycle. Second, we will elucidate the basis for regulation of expression of a key enzyme in purine nucleotide metabolism, IMPDH, interrogating both transcriptional and post-transcriptional steps. Inherited alterations in a regulatory domain of IMPDH and in proteins that direct spliceosome activation are associated with autosomal dominant retinitis pigmentosa, which leads to progressive blindness. We will look for commonalities between the two processes that might explain the highly specific pathological consequences of these disease mutations. Third, we will examine the functions of the hnRNP protein Hrp1 in the regulation of elongation and termination by RNA polymerase II. Hrp1 is structurally related to human hnRNP proteins in which inherited substitutions cause neurodegenerative disorders, including ALS and FTLD. Furthermore, Hrp1 exhibits a similar propensity to form intracellular aggregates, which are associated with pathology of the human proteins. A more complete understanding of these fundamental processes should lead to more accurate diagnosis and prognosis of diseases caused by alterations in nuclear RNA-binding proteins, and may ultimately result in new therapeutic approaches. Furthermore, the proposed studies will illuminate basic mechanisms of eukaryotic gene expression that can be exploited for synthetic biology and biotechnology.