All living processes are regulated by the dynamic interactions of proteins with small molecule ligands, partner proteins, nucleic acids, or other macromolecules. Instrumentation that enables quantitative analysis of the specificities and avidities of these interactions in vitro provides a physical foundation for understanding the intricate networks of reactions that contribute to complex biological processes. In this proposal, eleven faculty in the Departments of Biology and Biological Engineering at MIT request funding for the acquisition of an Octet RED96 instrument for the analysis of biomolecular interactions. This instrumentation exploits biolayer interferometry (BLI) to provide real time information on the binding of ligands in solution to immobilized molecules. The instrumentation accommodates a 96-well plate format for high- throughput analysis and is exceptionally versatile. Ligands can range from small molecules (>150 Da) up to very large protein or nucleic acid oligomers, and the acquisition of association and dissociation rate constants rapidly provides equilibrium constants over a broad dynamic range (10 pM - 1 mM) with very efficient sample requirements. Community access to hands-on use of this equipment will advance the pace and sophistication of multiple research programs and will be guaranteed by the central location of the instrument in the shared Biophysical Instrumentation Facility (BIF) in Building 68 of the MIT campus, which is run by a full-time technician (Ms. Debby Pheasant) and is directed by Professor Barbara Imperiali. The oversight committee for the acquisition and administration of all equipment in the BIF comprises Professors Barbara Imperiali (Chair), Robert Sauer, Amy E. Keating, Jacquin Niles and Ms. Debby Pheasant. !