Acts as an E3 ubiquitin-protein ligase, or as part of E3 complex, which accepts ubiquitin from specific E2 ubiquitin-conjugating enzymes and then transfers it to substrates (in vitro). Required for GLUTAMINE DUMPER 1(GDU1)-induced amino acid secretion and for amino acid homeostasis. Ubiquitinates GDU1 (in vitro). 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. Interacts with GDU1. A number of isoforms are produced. According to EST sequences. Expressed in the vascular tissues in both phloem and xylem parenchyma cells. The RING-type zinc finger domain mediates binding to an E2 ubiquitin-conjugating enzyme. Myristoylated (in vitro). No visible phenotype. Belongs to the RING-type zinc finger family. LOG2 subfamily.