Expression and interaction of the hepatitis C virus structural proteins and the 5′ untranslated regionin baculovirus infected cells

The structural proteins, core, E1 and a C-terminal truncated E2 (C-E1-E2p) as well as the 5′UTR linked to the core gene (5′UTR-C) of the hepatitis C virus were expressed in Sf9 cells. Expression of the C-E1-E2p polyprotein from a single vector resulted in expression of multiple forms suggesting that the cleavage of the polyprotein in the insect cells is incomplete. The structural proteins were expressed as insoluble forms and were solubilized by freeze/thaw cycles or detergent treatment. Analysis of the co-expressed (5′UTR-C and C-E1-E2p) proteins through a 20–60% sucrose gradient revealed that the core protein migrated rapidly into the gradient, in common with the sedimentation profile for core protein expressed from the core gene only. Neither E1 nor E2 proteins were involved in the core-core protein interaction. Expression of the 5′UTR-C in insect cells resulted in a high level of mRNA transcription but no translation of core protein, presumably due to a failure to initiate HCV translation by an internal ribosome entry mechanism, since the mRNA transcript was translated in vitro, suggesting that the 5′UTR can influence HCV tropism.