E3 ubiquitin-protein ligase that mediates ubiquitination and subsequent proteasomal degradation of target proteins (PubMed:12226665). E3 ubiquitin ligases accept ubiquitin from an E2 ubiquitin-conjugating enzyme in the form of a thioester and then directly transfers the ubiquitin to targeted substrates (PubMed:12226665). Mediates the ubiquitination and proteasomal-dependent degradation of NAC021/NAC022, a transcription activator that functions downstream of the auxin signals, thereby acting as a down-regulator of auxin signals (PubMed:12226665). Involved in the formation of lateral roots (PubMed:12226665). Is antagonist to SINAT1, SINAT2, SINAT3 and SINAT4 by suppressing FREE1 ubiquitination and degradation mediated by SINAT1, SINAT2, SINAT3 and SINAT4, and promoting FREE1 accumulation (PubMed:32786047). S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Homodimer; homodimerization is essential for its function. Interacts with UBC28 and NAC021/NAC022 (PubMed:12226665). Interacts with SINAT6 (PubMed:24350984). Interacts with ATG6 and TRAF1A (PubMed:28351989). Interacts with WAV3 (PubMed:22122664). Interacts with FREE1 (PubMed:32786047). Predominantly nuclear. Partially cytoplasmic. Multivesicular body (PubMed:32786047). Expressed at low level in the vascular tissue of mature roots. Expressed in lateral roots and in elongation zone of the main root upon stimulation by auxin. Colocalizes with NAC021/NAC022. By auxin (PubMed:12226665). Induced by salt stress (PubMed:24350984). The RING-type zinc finger domain is essential for ubiquitin ligase activity. The SBD domain (substrate-binding domain) mediates the homodimerization and the interaction with substrate proteins. It is related to the TRAF family. Belongs to the SINA (Seven in absentia) family.