Objective:To identify cellular factors in human liver that interact with hepatitis C virus (HCV) 5′ and 3′ untranslated regions (UTRs) and therefore possibly are involved in the regulation of HCV transcription or translation.Methods:We prepared cytoplasmic extracts from human liver biopsy samples and fractionated cellular factors on ion exchange columns. The various fractions from ion exchange columns were subjected to ultraviolet (UV) cross-linking with radiolabeled HCV 5′ and 3′ UTR RNA probes.Results:Two major 45- and 46-kd proteins that interacted specifically with the HCV 5′ and 3′ UTR were identified. Using Western blot and immunoprecipitation, these proteins were identified as the La antigen.ConclusionOur results demonstrate that the La protein from human liver biopsy cells interacts specifically with the U-rich region in the positive strand of the HCV 3′ UTR.Journal of Human Virology 1999;2:296-307 © Lippincott Williams & Wilkins, Inc.