Otubain 1, also known as OTUB1, is a member of the OTU (ovarian tumor) superfamily of predicted cysteine proteases and inhibits cytokine gene transcription in the immune system via its interaction with an ubiquitin protease and E3 ubiquitin ligase. This protein is a highly specific ubiquitin iso-peptidase, and cleaves ubiquitin from branched poly-ubiquitin chains but not from ubiquitinated substrates. It is proposed to function in specific ubiquitin-dependent pathways, possibly by providing an editing function of polyubiquitin chain growth.