Probable E3 ubiquitin-protein ligase which mediates ubiquitination and subsequent proteasomal degradation of target proteins. 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. Widely expressed. Expressed in root, stem, cauline and rosette leaf, seedling and flower (at protein level). Constitutively expressed throughout development post-germination (at protein level). Belongs to the UPL family. TOM1/PTR1 subfamily.