Accepts the ubiquitin from the E1 complex and catalyzes its covalent attachment to other proteins. Involved in the formation of multiubiquitin chains. Signal the protein for selective degradation. 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. Up-regulated by syringolin, a cell death-inducing chemical. Belongs to the ubiquitin-conjugating enzyme family. This protein has been named UBC13 according to the nomenclature proposed in PubMed:16339806, but it is not the same as the UBC13 described in several publications that correspond to the protein named UBC35 in our nomenclature.