Cyclin B1, encoded by the CCNB1 gene, is regulated by H2B ubiquitination at its promoter by the E2 enzyme radiation sensitive 6 (RAD6) in esophageal squamous cell carcinoma (ESCC), affecting ESCC cell proliferation [205, 368]. The gene discussed is H2BC21; the disease is esophageal squamous cell carcinoma.