Talk by: Allen Nicholson, Dean, College of Science & Technology, Temple University

Title: The ribonuclease III superfamily: forms and functions in RNA maturation, RNA decay, and gene silencing

Abstract: Ribonucleases are a functionally and mechanistically diverse group of enzymes that catalyze RNA cleavage reactions important for RNA maturation, RNA degradation, antiviral defense, and gene silencing. Ribonucleases are under intensive investigation in many laboratories, with the goal to understand their roles in gene expression and cell function in both the normal and disease states. Also, specifically engineered ribonucleases are being assessed as potent anticancer agents. My research group is specifically interested in the ribonuclease III (RNase III) superfamily of double-stranded(ds)-RNA-specific endonucleases. These nucleases are highly conserved in prokaryotic and eukaryotic cells. We are studying primarily the mechanism of action of bacterial RNase III orthologs, which exhibit a conserved dsRNA-binding domain (dsRBD) and a nuclease domain. In particular we are characterizing the active site components of Escherichia coli RNase III and determining divalent metal ion function in phosphodiester hydrolysis. We also are characterizing the sequence and structural features in RNase III substrates that confer reactivity and cleavage site selectivity. We have determined that specific Watson-Crick base-pair sequences act as antideterminants (i.e. inhibitors) of RNase III recognition and cleavage. These sequence elements appear to play a vital role in cleavage site selection as well as in protecting other intracellular dsRNAs from inappropriate cleavage. Current research is extending the findings on bacterial RNase III to other orthologs, including Dicer, which is involved in the generation of siRNAs in the RNA interference (RNAi) pathway.