Focus issue: systems analysis of protein phosphorylation.

Kinases and phosphatases are key regulatory molecules that participate in most cell signaling pathways. Systems-level analyses are providing new insights into phosphorylation sites and kinase specificity, and phosphoproteomic analyses are creating not just a wealth of data, but are also revealing rich revelations about cellular behavior, cellular responses to changing environmental conditions, and mechanisms of disease. Phosphatases are not merely signal terminators, but play active roles in signal transduction and are especially important in redox signaling. In this Focus Issue, Science Signaling highlights protein phosphorylation as the center of the signaling universe.