These values were 2.1–6.4 times and 1.4–2.9 times higher than those (1.4–1.9×10−3 base substitutions/site/year) previously obtained in chimpanzees [15], [16] and in a patient [14] with chronic hepatitis C. Since we previously found that the mutation rates of genome-length HCV RNAs were 4.4–7.4×10−3 and 2.5–3.7×10−3 base/substitutions/site/year in 5′-terminus-NS2 regions and NS3-NS5B regions, respectively, using HuH-7-derived cell culture systems [21], most of the mutation rates were proved not to change, regardless of the cell type. The gene discussed is KRAS; the disease is chronic hepatitis C virus infection.