FBXO5 and breast cancer: Moreover, PUMA-mediating Rad51 ubiquitination was dependent on EMI1 (early mitotic inhibitor 1; also known as FBXO5 and FBX5), an F-box protein,11 which has been shown to be involved in the regulation of Rad51 ubiquitination and HR DNA repair in breast cancer.12 We found that PUMA formed a ternary complex with Rad51 and EMI1 in the cytoplasm, and facilitated Rad51 ubiquitination by EMI1 in PSCs and HPCs.