Two-step affinity purification of the hepatitis C virus ribonucleoprotein complex.

Positive-strand RNA viruses replicate their RNA genome within a ribonucleoprotein (RNP) complex that is associated with cellular membranes. We used a two-step method of purification to isolate hepatitis C virus (HCV) RNP complexes from human hepatoma cell line Huh7, which stably expresses HCV subgenomic replicons. The procedure involved hybridization of replicon-expressing cellular lysates with oligonucleotides tagged with biotin and digoxigenin at their respective termini complementary to subgenomic replicon RNA followed by avidin-agarose enrichment of the mixture and subsequent immunoprecipitation of biotin-eluted material with anti-digoxigenin antibody. The immunoprecipitates were immunoblotted with antisera against HCV nonstructural (NS) proteins. The analysis revealed the association of all the HCV NS proteins (NS3, NS4a, NS4b, NS5a, and NS5b) that are encoded by the subgenomic replicon RNA. The HCV RNP complex migrated in a native polyacrylamide gel with an approximate molecular mass of 450 kD. The association of these viral proteins in the RNP complex reinforces the widely acknowledged notion that RNA viruses accomplish replication within a membranous RNP complex.