Ubc9 binding site mutations, as well as disease associated mutation in the BRCA1 RING domain (C61G), disrupted the ability to regulate Ubc9-mediated estrogen-induced ER-α transcriptional activity in breast cancer cells [30] but did not disrupt SUMO-1 binding [28] nor auto ubiquitination activity of BRCA1 [30]. Here, UBE2I is linked to breast cancer.