Receptor for activated thrombin coupled to G proteins that stimulate phosphoinositide hydrolysis. Interacts with INSC/inscuteable and probably GPSM2. Highest expression in the megakaryocytes of the bone marrow, lower in mature megakaryocytes, in platelets and in a variety of other tissues such as heart and gut. A proteolytic cleavage generates a new N-terminus that functions as a tethered ligand. Belongs to the G-protein coupled receptor 1 family.