ROC 1 and ROC 2 are the two highly conserved RING finger proteins that are homologous to APC 11, a subunit of the anaphase promoting complex(APC). ROC 1 and ROC 2 commonly interact with all cullins while APC 11 specifically interacts with APC 2, a cullin related APC subunit. ROC 1 and APC 11 immunocomplexes can catalyze isopeptide ligations to form polyubiquitin chains in an E1 and E2 dependent manner. ROC 1 is thought to play a unique role in the ubiquitination reaction by heterodimerizing with cullin 1 to catalyze ubiquitin polymerization.