Receptor for activated thrombin or trypsin coupled to G proteins that stimulate phosphoinositide hydrolysis. May play a role in platelets activation. Widely expressed, with highest levels in lung, pancreas, thyroid, testis and small intestine. Not expressed in brain, kidney, spinal cord and peripheral blood leukocytes. Also detected in platelets. A proteolytic cleavage generates a new N-terminus that functions as a tethered ligand. Belongs to the G-protein coupled receptor 1 family.