Used in molecular biology as a tool for studying RNA structure and function. It can be incorporated into RNA molecules to act as a photoaffinity label, enabling the identification of RNA-protein interactions. Also employed in crosslinking experiments to analyze RNA secondary structures and dynamics. Additionally, it serves as a substrate for certain enzymes in biochemical assays to investigate enzyme specificity and activity. Furthermore, 4-Thiouridine is utilized for metabolic labeling of nascent RNA transcripts, allowing the study of transcription rates, RNA processing, and decay dynamics through techniques like SLAM-seq.