PROJECT SUMMARY Our research aims to delineate the dynamics of RNA binding proteins (RBPs) and their associated complexes in RNA metabolism. Although critical for cellular function, the dynamics by which RBPs interact with their substrates are poorly understood. To address this problem, we develop and apply novel quantitative approaches to characterize dynamic RNA-protein interactions in vitro and in cells. Planned research focuses on three questions: (i) how does the dynamics of the RNA helicases Ded1p and DDX3X dictate their cellular function, (ii) how do the components of the TRAMP-exosome machinery coordinate their activities in vitro and in the cell, and (iii) how do RNA-interaction dynamics of RBPs with multiple RNA binding domains determine cellular RBP function. Here we will focus on the RBP IMP1. The planned research is expected to provide fundamentally new insight into RNA biology with direct implications for understanding molecular mechanisms of tumorigenesis and viral infectious diseases.