The function of RNF19B (ring finger protein 19B, ENSG00000116514) is as follows. E3 ubiquitin-protein ligase which accepts ubiquitin from E2 ubiquitin-conjugating enzymes UBE2L3 and UBE2L6 in the form of a thioester and then directly transfers the ubiquitin to targeted substrates, such as UCKL1 (PubMed:16709802, PubMed:27485036). Involved in the cytolytic activity of natural killer cells and cytotoxic T-cells (PubMed:10438909). Protects against staurosporin-induced cell death (PubMed:27485036). {ECO:0000269|PubMed:10438909, ECO:0000269|PubMed:16709802, ECO:0000269|PubMed:27485036}.