1 From the ‡Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, California 94143;. Electronic address: chalkley@cgl.ucsf.edu.
2 ¶Department of Genome Sciences, University of Washington, Seattle, Washington 98195.
3 ‖Proteomics Platform, Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142.
4 Donnelly Centre, University of Toronto, Toronto, Ontario M5S 3E1, Canada.