Establishment of an in vitro assay system for screening hepatitis C virus protease inhibitors using high performance liquid chromatography: Kenji Sudo1,3, Hiroshi Inoue1, Yasuaki Shimizu2, Kayo Yamaji2, Kenji Konno1, Shiro Shigeta3, Takashi Kaneko4, Tomoyuki Yokota1, and Kunitada Shimotohno4, Rational Drug Design Laboratories1, Fukushima 960-12, Molecular Medicine Research Laboratories, Yamanouchi Pharmaceutical Co. Ltd.2, Tsukuba-shi, Ibaraki 305, Department of Microbiology, Fukushima Medical College3, Fukushima 960-12, Virology Division, National Cancer Center Research Institute4, Tokyo 104, Japan