N-(Azido-PEG3)-N-Fluorescein-PEG3-acid is a PEG-based PROTAC linker which contains azide, fluorescein and carboxylic acid moieties.In Vitro: PROTACs contain two different ligands connected by a linker; one is a ligand for an E3 ubiquitin ligase and the other is for the target protein. PROTACs exploit the intracellular ubiquitin-proteasome system to selectively degrade target proteins.