Deubiquitinating enzyme involved in protein homeostasis maintenance; transcription; cytoskeleton regulation; myogenesis and degradation of misfolded chaperone substrates. Binds long polyubiquitin chains and trims them; while it has weak or no activity against chains of 4 or less ubiquitins. Involved in degradation of misfolded chaperone substrates via its interaction with STUB1/CHIP: recruited to monoubiquitinated STUB1/CHIP; and restricts the length of ubiquitin chain attached to STUB1/CHIP substrates and preventing further chain extension. In response to misfolded substrate ubiquitination; mediates deubiquitination of monoubiquitinated STUB1/CHIP. Interacts with key regulators of transcription and represses transcription: acts as a histone- binding protein that regulates transcription. {ECO:0000269|PubMed:12297501; ECO:0000269|PubMed:16118278; ECO:0000269|PubMed:17696782; ECO:0000269|PubMed:23625928}.