RAD23B is a multifunctional protein with primary roles in DNA repair, protein degradation, and histone modification. In nucleotide excision repair (NER), RAD23B functions as a core component of the XPC complex, which recognizes bulky DNA lesions including UV damage and cisplatin-induced adducts 1. The XPC-RAD23B heterodimer initiates global genome NER by sensing DNA helix distortions and preferentially binds to damaged double-stranded DNA 2. RAD23B cooperatively enhances UV-DDB binding to facilitate cyclobutane pyrimidine dimer detection through one-dimensional DNA diffusion 2. Beyond NER, RAD23B acts as a polyubiquitin chain receptor that bridges ubiquitinated substrates to the 26S proteasome for degradation, with multivalent ubiquitin-associated domains enabling ubiquitin-chain-dependent phase separation of nuclear proteasomes under stress 3. Additionally, RAD23B demethylates histone H4K20 residues to regulate transcription of coding genes and repetitive elements. Clinically, RAD23B stabilization by deubiquitinase PSMD7 correlates with gastric cancer progression and cisplatin resistance, suggesting RAD23B's role in chemotherapy sensitivity 4. In breast cancer, reduced nuclear RAD23B associates with increased invasiveness and higher histological grades, implying a tumor suppressor function 5. Conversely, circular RAD23B (circ-RAD23B) acts as an oncogene in non-small cell lung cancer through miRNA sponging mechanisms 6.