The aim of this proposal is to request funding for a new state-of-the-art nano UPLC Q-Exactive Plus mass spectrometer from Thermo Scientific, which we plan to integrate into the Proteome Exploration Laboratory (PEL) of the Beckman Institute at the California Institute of Technology (Caltech) to replace our existing Orbitrap Classic mass spectrometer, which is now reaching the maximum expected lifetime and thus, Thermo is phasing out their support on this instrument. We request funding because technological limitations of our current instruments are no longer meeting methodological demands of the increasing number of users, hampering the progress of NIH-funded projects in the laboratories of our collaborators. Due to technological innovations, the Orbitrap Classic can effectively no longer compete with current state-of-the-art technology as a result of the tremendous instrumentation developments during the past years; and is therefore hindering our advancement in the field of proteomics. The Q-Exactive Plus also offers unique measurement capabilities due to its quadrupole filter rather than an ion trap, which will enable many projects t the PEL that we can currently not carry out. The PEL was established in 2007 and is the only resource center at Caltech where mass spectrometry-based proteomic analyses can be performed. The PEL was initially established to primarily collaborate with students and postdoctoral fellows of the Caltech community to develop new methods and advance their proteomics-related research. Due to its commitment to excellence, the PEL is frequently able to analyze difficult samples that typical facilities may not be successful with. As a consequence, the PEL has developed into a center that is also sought out by other researchers as well, local and state-wide. The overwhelming success of our proteomics setup has steadily increased the demand at the PEL and continues to increase further. The main long-term objective of the PEL is to enable the in-depth elucidation and quantification of proteomes, subproteomes and individual proteins to gain fundamental insights into biological regulatory processes. A common experimental paradigm is to monitor global protein changes that occur after either treating cells with drugs or natural ligands; or subjecting them to an environmental or genetic perturbation. A Q-Exactive Plus mass spectrometer coupled with the EASY nano UPLC system, working in concert with our existing bioinformatics pipeline, will play a vital role in advancing projects tha span a broad range of fundamental (developmental processes) and applied studies (cancer, bacterial infections). Fundamental insights into any of these areas will help prevent and/or cure diseases that have previously been considered incurable.