The function of OTUB1 (OTU deubiquitinase, ubiquitin aldehyde binding 1, ENSG00000167770) is as follows. Hydrolase that can specifically remove 'Lys-48'-linked conjugated ubiquitin from proteins and plays an important regulatory role at the level of protein turnover by preventing degradation (PubMed:12401499, PubMed:12704427, PubMed:14661020, PubMed:23827681). Regulator of T-cell anergy, a phenomenon that occurs when T-cells are rendered unresponsive to antigen rechallenge and no longer respond to their cognate antigen (PubMed:14661020). Acts via its interaction with RNF128/GRAIL, a crucial inductor of CD4 T-cell anergy (PubMed:14661020). Isoform 1 destabilizes RNF128, leading to prevent anergy (PubMed:14661020). In contrast, isoform 2 stabilizes RNF128 and promotes anergy (PubMed:14661020). Surprisingly, it regulates RNF128- mediated ubiquitination, but does not deubiquitinate polyubiquitinated RNF128 (PubMed:14661020). Deubiquitinates estrogen receptor alpha (ESR1) (PubMed:19383985). Mediates deubiquitination of 'Lys-48'-linked polyubiquitin chains, but not 'Lys-63'-linked polyubiquitin chains (PubMed:18954305, PubMed:19211026, PubMed:23827681). Not able to cleave di-ubiquitin (PubMed:18954305, PubMed:23827681). Also capable of removing NEDD8 from NEDD8 conjugates, but with a much lower preference compared to 'Lys-48'-linked ubiquitin (PubMed:18954305, PubMed:23827681). {ECO:0000269|PubMed:12401499, ECO:0000269|PubMed:12704427, ECO:0000269|PubMed:14661020, ECO:0000269|PubMed:18954305, ECO:0000269|PubMed:19211026, ECO:0000269|PubMed:19383985, ECO:0000269|PubMed:23827681}. Plays a key non-catalytic role in DNA repair regulation by inhibiting activity of RNF168, an E3 ubiquitin-protein ligase that promotes accumulation of 'Lys-63'-linked histone H2A and H2AX at DNA damage sites (PubMed:20725033, PubMed:22325355). Inhibits RNF168 independently of ubiquitin thioesterase activity by binding and inhibiting UBE2N/UBC13, the E2 partner of RNF168, thereby limiting spreading of 'Lys-63'-linked histone H2A and H2AX marks (PubMed:20725033, PubMed:22325355). Inhibition occurs by binding to free ubiquitin: free ubiquitin acts as an allosteric regulator that increases affinity for UBE2N/UBC13 and disrupts interaction with UBE2V1 (PubMed:20725033, PubMed:22325355). The OTUB1-UBE2N/UBC13-free ubiquitin complex adopts a configuration that mimics a cleaved 'Lys48'- linked di-ubiquitin chain (PubMed:20725033, PubMed:22325355). Acts as a regulator of mTORC1 and mTORC2 complexes (PubMed:29382726, PubMed:35927303). When phosphorylated at Tyr-26, acts as an activator of the mTORC1 complex by mediating deubiquitination of RPTOR via a non- catalytic process: acts by binding and inhibiting the activity of the ubiquitin-conjugating enzyme E2 (UBE2D1/UBCH5A, UBE2W/UBC16 and UBE2N/UBC13), thereby preventing ubiquitination of RPTOR (PubMed:35927303). Can also act as an inhibitor of the mTORC1 and mTORC2 complexes in response to amino acids by mediating non-catalytic deubiquitination of DEPTOR (PubMed:29382726). {ECO:0000269|PubMed:20725033, ECO:0000269|PubMed:22325355, ECO:0000269|PubMed:29382726, ECO:0000269|PubMed:35927303}.