Ring Box Protein 1 (RBX1)

RING-box protein 1 plays a unique role in the ubiquitination reaction by heterodimerizing with cullin-1 to catalyze ubiquitin polymerization. It also may be involved in the regulation of protein turn-over.The ROC1 and ROC2 proteins commonly interact with all cullins. Yeast ROC1 encodes an essential gene whose reduced expression resulted in multiple, elongated buds and accumulation of Sic1 and Cln2 proteins.

ROC1 and APC11 immunocomplexes can catalyze isopeptide ligations to form polyubiquitin chains in an E1- and E2-dependent manner. ROC1 mutations completely abolished their ligase activity without noticeable changes in associated proteins. Ubiquitination of phosphorylated I-kappa-B-alpha can be catalyzed by the ROC1 immunocomplex in vitro.