Why do siRNA screens? You may know the basic elements of a cellular signaling pathway but would like to know what other processes are required for or modulate that signaling process. Alternatively, in different cell contexts (e.g. pancreatic beta cells vs. cardiac myocytes) the process may utilize different subtypes of key signaling elements. A whole genome siRNA screen would point you to both unknown genes affecting the process or to specific subtypes of large gene families that are critical in your cell system. This is of importance biologically but it can also reveal novel drug targets that may be attacked chemically in a drug discovery effort. To support latter, the CCG also provides a "subset" screening library termed the "druggable genome" collection, which includes many common Pharma drug targets such as GPCRs, kinases, phosphatases, and ion channels. It also includes proteases and elements of the ubiquitin proteasome mechanisms.