Fine epitope mapping using yeast display. The anti-HCV core antigen MAb has been mapped to aa 32 to 36, the anti-HCV NS4 MAb to aa 1697 to 1708, the HCV NS3 cAb to aa 1190 to 1216, and the HCV NS5 cAb to aa 2382 to 2408. To fine map the epitopes, alanine scanning combined with yeast display was used to probe the epitopes at the individual amino acid level. Each amino acid of the epitope fragment was substituted with alanine. For example, HCV NS5 aa 2382 to aa VOL. 17,2010 cAbs AGAINST HCV NS3, NS4, NS5, AND CORE ANTIGENS 1043 2408 had alanine substituted at each position of the epitope, with the exclusion of aa 2382, which was alanine in the wild type. These yeast cells expressing alanine mutations were cultured, induced, and analyzed by FACs Calibur to determine which alanine mutant had lost the antibody binding activity, indicating that the mutated amino acid was part of the antibody binding epitope. The **data** showed that HCV NS5 antigen residues Pro2390, Leu2391, Glu2392, Gly2393, Glu2394, Pro2395, Asp2397, Pro2398, and Leu2400 were the anti-HCV NS5 chimeric antibody binding sites (Fig. 5).