4-Thiouridine 5′-triphosphate (4-Thio-UTP) tetralithium is a potent P2Y 2 and P2Y 4 receptor agonist, with EC 50 s of 35 and 350 nM for hP2Y 2 and hP2Y 4 , respectively. 4-Thiouridine 5′-triphosphate tetralithium can be used in the study of crosslinking experiments, labeling of transcriptional complex.