How do cells recognize external environments and what are the targets to which signals are transmitted in response to the external environment? In an effort to answer these questions, it is important to delineate the specific interactions (selection of information) between biomacromolecules such as proteins, nucleic acids and membrane components. In this laboratory, attempts are being made to clarify the mechanisms concerning molecular recognition and the responses to external environments by determining the three-dimensional structure of biomolecular complexes and the physicochemical features of these interactions using NMR spectroscopy, a method which provides an excellent means for the determination of three-dimensional macromolecular structures and the analysis of interactions under physiological conditions.