HOIP-UB is a binding domain on E3 ubiquitin-protein ligase RNF31 like proteins. E3 ubiquitin-protein ligase RNF31 is often referred to as HOIL-1L binding partner. The interaction of HOIL-1L and HOIP is thus via the UBL-UBA interaction. this interaction is important in E3 complex formation and the subsequent activation of NF-kappaB [1]. This family contains two UBA-like domains.

1: A non-canonical UBA-UBL interaction forms the linear-ubiquitin-chain assembly complex. Yagi H, Ishimoto K, Hiromoto T, Fujita H, Mizushima T, Uekusa Y, Yagi-Utsumi M, Kurimoto E, Noda M, Uchiyama S, Tokunaga F, Iwai K, Kato K; EMBO Rep. 2012;13:462-468. PMID:22430200