Core component of a Cul9-RING ubiquitin-protein ligase complex composed of CUL9 and RBX1 (PubMed:38605244). The CUL9-RBX1 complex mediates ubiquitination and subsequent degradation of BIRC5 and is required to maintain microtubule dynamics and genome integrity. Acts downstream of the 3M complex, which inhibits the ubiquitination of BIRC5 (PubMed:24793696). The CUL9-RBX1 complex also mediates mono- ubiquitination of p53/TP53 (PubMed:38605244). Acts as a cytoplasmic anchor protein in p53/TP53-associated protein complex. Regulates the subcellular localization of p53/TP53 and its subsequent function (PubMed:12526791, PubMed:17332328). Ubiquitinates apurinic/apyrimidinic endodeoxyribonuclease APEX2 (PubMed:38605244). Ubiquitination by the CUL9-RBX1 complex is predominantly mediated by E2 ubiquitin-conjugating enzymes UBE2L3 and UBE2D2 (PubMed:38605244). {ECO:0000269|PubMed:12526791, ECO:0000269|PubMed:17332328, ECO:0000269|PubMed:24793696, ECO:0000269|PubMed:38605244}. This is the function of ENSG00000112659 (CUL9, cullin 9).