This proposal is to study proteins that are important in the regulation of gene expression by binding to messenger RNA. These proteins are involved in regulating genes that control cell proliferation, inflammation and also viral genome replication. We will determine the molecular basis for their interactions using tools which allow us to measure binding affinities and molecular shapes. We will also examine the impact of protein modifications or presence of microRNA molecules on the binding interactions. In this way we will discover some of the rules that dictate the regulation of gene expression at the level of messenger RNA.