Over the past few years there has been tremendous advances in the sensitivity of mass spectrometers for peptide sequencing, the ability of parent ion scanning approaches to rapidly detect and identify a plethora of protein posttranslational modifications and the promise of gentle ionization techniques to extend mass spectroscopy into the realm of non-covalent protein interactions and folding. These techniques have been disseminated slowly because of the small number of laboratories with demonstrated track record in these new techniques. The current proposal is intended to bring state-of-the-art mass spectroscopy to Yale University through the purchase of a QTOF mass spectrometer. This instrument will support research in 10 institutions that do not currently have a comparable instrument. The projects include a broad spectrum of biological research areas including tRNA synthesis; pre- mRNA maturation; early neurogenesis; the control of cellular differentiation and growth; intracellular membrane transport; protein structure and dynamics; the generation of antigen receptor diversity; and the role of cell surface glycosylation in establishing cellular identity.