Our research focuses on the elucidation of three-dimensional (3D) solution structure and dynamics of proteins and complexes, involving protein-protein and protein-nucleic interactions, as a means of understanding the mechanism of action for these systems. The nuclear magnetic resonance (NMR) technique is unique among biophysical methods in its ability to provide atomic-resolution information on such systems in solution. The primary targets of our efforts are proteins involved in the transmission of signals between and within cells and proteins controlling gene expression. By investigating the structural biology of these systems, our studies can provide insight into the complex regulation of cell replication, which is crucial to the development and proliferation of cancer. Determining 3D solution structures requires state-of-the-art capabilities in multidimensional, triple- and quadruple-resonance NMR spectroscopy and isotopic labeling of proteins and nucleic acids. We devote a part of our efforts to the development of improved NMR techniques and hardware, as well as protein engineering. Recent work in our laboratory includes the establishment of procedures for the preparation of triply labeled proteins (e.g., N15, C13, and H2) both in uniform patterns and with selective methyl protonation in an otherwise N/C/D background. In this reporting period, our research has involved the transcription antiterminator NusB, hepatocyte growth factor (HGF), hematopoetic cell kinase (Hck), and human interleukin-13. Preliminary work is underway on systems related to apoptosis. We have determined the high-resolution structures and investigated backbone dynamics and complexes of these proteins with their respective ligands or receptors.