PROCESSING IN THE HEPATITIS-C VIRUS E2-NS2 REGION - IDENTIFICATION OFP7 AND 2 DISTINCT E2-SPECIFIC PRODUCTS WITH DIFFERENT C-TERMINI

The hepatitis C virus (HCV) H strain polyprotein is cleaved to produce at least nine distinct products: NH2-C-E1-E2-NS2-NS3-NS4A-NS4B-NS5A-N S5B-COOH. In this report, a series of C-terminal truncations and fusio n with a human c-myc epitope tag allowed identification of a tenth HCV -encoded cleavage product, p7, which is located between the E2 and NS2 proteins. As determined by N-terminal sequence analysis, p7 begins wi th position 747 of the HCV H strain polyprotein. p7 is preceded by a h ydrophobic sequence at the C terminus of E2 which may direct its trans location into the endoplasmic reticulum, allowing cleavage at the E2/p 7 site by host signal peptidase. This hypothesis is supported by the o bservation that cleavage at the E2/p7 and p7/NS2 sites in cell-free tr anslation studies was dependent upon the addition of microsomal membra nes. However, unlike typical cotranslational signal peptidase cleavage s, pulse-chase experiments Indicate that cleavage at the E2/p7 site is incomplete, leading to the production of two E2-specific species, E2 and E2-p7. Possible roles of p7 and E2-p7 in the HCV life cycle are di scussed.