Previous studies have revealed that RBX1 is a growth essential gene in yeast, Caenorhabditis elegans, Drosophila, mouse and several human cancer cell lines.10,28,29 In yeast, ROC1 is required for the ubiquitination of the cyclin-dependent kinase inhibitor Sic1 during the G1 to S phase cell cycle transition. This evidence concerns the gene RBX1 and cancer.