Alternate translation occurs within the core coding region of the hepatitis C viral genome

The majority of hepatitis C virus (HCV) isolates contain an open reading frame (ORF) overlapping with the core coding sequences in the +1 frame, which was assumed to be untranslated. We present evidence supporting the expression of this ORF (designated core+1 ORF) via novel translation mechanisms. First, fusion of the luciferase gene with the HCV-1 core+1 ORF followed by in vitro translation resulted in the synthesis of a chimeric protein (core+1-luciferase) that exhibited approximately 54% luciferase activity relative to the positive control (core-luciferase). Second, antisera raised against two different synthetic core+1 peptides recognized the previously identified p16 (but not p21) core protein band expressed from HCV-1, indicating the presence of epitopes from the core+1 ORF within the p16 protein. Third, HCV-positive sera specifically recognized lysates of Escherichia coli cells expressing recombinant core+1 protein, suggesting the presence of anti-core+1 antibodies in HCV-infected patients. Finally, luciferase tagging experiments designed to assess for -1 frameshifting combined with site-directed mutagenesis experiments supported the presence of +1/-1 ribosomal frameshift translation mechanisms within the core coding region. In conclusion, our data provide evidence for novel translation mechanisms within the core coding region and demonstrate the expression of the core+1 ORF, at least for some HCV isolates.