Disclosed herein include methods, compositions, and kits suitable for use in detecting the activation level of a signal transducer. In some embodiments, there are provided synthetic protein circuits wherein recruitment of synthetic protein circuit components to an association location upon activation of a signal transducer generates an active effector protein. The effector protein can be configured to carry out a variety of functions when in an active state, such as, for example, inducing cell death. Methods of treating a disease or disorder characterized by aberrant signaling are provided in some embodiments.