Identification of 3CLpro cleavage sites by trans-cleavage assay. In vitro-translated substrates encoded by HCV 229E ORF 1a were incubated with buffer (lanes 1, 3, 5, and 7) or buffer containing recombinant 3CLpro (lanes 2, 4, 6, and 8) for 90 min at 30°C as described in Materials and Methods. The reaction mixtures were separated by SDS–17.4% polyacrylamide gel electrophoresis and analyzed by autoradiography. Sizes of molecular mass markers (lane M) (CFA 626; Amersham Pharmacia Biotech) are given on the left, and the major cleavage products are indicated by arrows on the right.