Description
There are two main classes of DUB, cysteine proteases and metalloproteases. Ubiquitin specific protease 21 (USP21) is a member of the cysteine protease enzyme family and cloning of the gene was first described by Gong et al. (2000). USP21 cleaves ubiquitin polymers, and with reduced activity also targets the UBL ISG15 but not NEDD8 (Ye et al., 2011). USP21 has been shown to be involved in the regulation of transcriptional initiation through the deubiquitylation of histone H2A as well as playing a role in the regulation of tumour necrosis factor α (TNFα) induced nuclear factor κβ (NF-κβ) activation by deubiquitylating receptor-interacting protein 1 (RIP1) (Nakagawa et al., 2008; Xu et al., 2010)