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TAK1-binding protein 2 (TAB2) and/or TAB3, as part of a complex that also contains TAK1 and TAB1, binds polyubiquitinated TRAF6. The TAB2 and TAB3 regulatory subunits of the TAK1 complex contain C-terminal Npl4 zinc finger (NZF) motifs that recognize with Lys63-pUb chains (Kanayama et al. 2004). The recognition mechanism is specific for Lys63-linked ubiquitin chains (Kulathu Y et al 2009). TAK1 can be activated by unattached Lys63-polyubiquitinated chains when TRAF6 has no detectable polyubiquitination (Xia et al. 2009) and thus the synthesis of these chains by TRAF6 may be the signal transduction mechanism.As a de-ubiquitinating/de-ISGylating enzyme, severe acute respiratory syndrome coronavirus type 1 (SARS-CoV-1) 1a-encoded papain-like protease (PLPro or nsp3) antagonizes the host type I interferon (IFN) response by removing Lys63-linked ubiquitin chains of TRAF3 and TRAF6 (Li SW et al. 2016).