The La protein from human liver cells interacts specifically with the U-rich region in the hepatitis C virus 3' untranslated region.

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 I-ICV 5' and 3' UTR were identified. Using Western blot and immunoprecipitation, these proteins were identified as the La antigen. Conclusion: Our 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.