Ubiquitin-conjugating enzyme E2 that specifically acts with HECT-type and RBR family E3 ubiquitin-protein ligases. Does not function with most RING-containing E3 ubiquitin-protein ligases because it lacks intrinsic E3-independent reactivity with lysine: in contrast, it has activity with the RBR family E3 enzymes, such as PRKN and ARIH1, that function like RING-HECT hybrids. Accepts ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. In vitro catalyzes 'Lys-11'-linked polyubiquitination. Involved in the selective degradation of short-lived and abnormal proteins. Down-regulated during the S-phase it is involved in progression through the cell cycle. Regulates nuclear hormone receptors transcriptional activity. May play a role in myelopoiesis. S-ubiquitinyl-[E1 ubiquitin-activating enzyme]-L-cysteine + [E2 ubiquitin-conjugating enzyme]-L-cysteine = [E1 ubiquitin-activating enzyme]-L-cysteine + S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine. Protein modification; protein ubiquitination. Interacts with PRKN; involved in ubiquitination and degradation of misfolded proteins. Interacts with UBE3A. Interacts with CCNB1IP1, CBL, ZAP70, RNF19A, RNF19B and RNF144B. Interacts with ARIH1. Interacts with ARIH2 (via RING-type 1). Interacts with NCOA1; they functionally interact to regulate progesterone receptor transcriptional activity. Interacts with NDFIP1 (via N-terminus); the interaction mediates recruitment of UBE2L3 to ITCH and causes MAP3K7 ubiquitination. In contrast to other ubiquitin-conjugating enzymes E2, residues essential for lysine reactivity are absent: Pro and a His residues are present instead of an Asp and an Asp residues in positions 88 and 119, respectively. Ubiquitinated. The alteration of UBE2L3 protein levels during the S-phase of the cell cycle is due to ubiquitin-dependent proteasomal degradation. Autoubiquitinated in vitro. Belongs to the ubiquitin-conjugating enzyme family.