USP7 (ubiquitin specific peptidase 7) is a deubiquitinating enzyme that prevents protein degradation by removing poly-ubiquitin chains from its substrates. It regulates stability of a number of human transcription factors and tumor suppressors and plays a critical role in the development of several types of cancer, including prostate and small cell lung cancer.USP7 regulates Pol-eta (DNA polymerase eta) stability through both indirect and direct mechanisms. It regulates the stability of the DNA maintenance methyltransferase. Diseases associated with USP7 include UV-sensitive syndrome.