To construct a hepatitis C virus (HCV) genotype 2a monocistronic replicon and investigate its replication capabilities in the human hepatocarcinoma cell lines, Huh7.5 and Huh7.1, in order to determine its potential as a molecular tool for future in vitro studies of HCV replication and selection studies for putative anti-HCV drugs. Site-directed mutagenesis was used to delete the Core-E1-E2-p7-NS2 fragment (about 3090 bp) from plasmid pJ6JFH1BlaRL. The resultant trianglepJ6JFH1BlaRL plasmid was digested with AgeI and AvrII to release the cDNA fragment (hereafter, referred to as fragment L) containing partial 5'-untranslated region (UTR), the first 12 amino acid (aa) of HCV Core coding sequence, full-length coding sequences for the blasticidin-resistance gene, Renilla luciferase, foot-and-mouth disease virus (FMDV) 2a antiprotease and ubiquitin, and partial coding sequence for HCV NS3. To generate the monocistronic replicon, pSGRmJFH1BlaRL, fragment L was ligated into the pSGR-JFH1 vector that had been digested with AgeI and AvrII to remove the partial 5'-UTR, the first 19 aa of HCV Core coding sequence, the full-length coding sequence for the neomycin phosphotransferase II gene, the internal ribosomal entry site from encephalomyocarditis virus, and partial HCV NS3 coding sequence. A replication-defective mutant replicon, pSGRmJFH1BlaRL/GND, was constructed by a similar procedure using the pSGR-JFH1/GND vector. Fragment L was confirmed in both constructs by sequencing. Replicon RNAs were prepared from XbaI-linearized plasmid DNA templates with Invitrogen's T7 MEGAscript kit, and were purified by DNase I treatment and LiCl precipitation. RNAs were quanti?ed by optical density, and the quality and concentration were con?rmed by agarose gel electrophoresis. Replicon RNAs were transfected into Huh7.5 and Huh7.1 cells using Invitrogen's DMRIE-C transfection reagent at a ratio of 5 mug of lipid to 1mug of RNA. Time course assay of Renilla luciferase activity indicated the replicon's replication function. The pSGRmJFH1BlaRL monocistronic replicon and pSGRmJFH1BlaRL/GND replication-defective mutant replicon were successfully constructed. The pSGRmJFH1BlaRL replicon was replication-proficient in Huh7.5 and Huh7.1 cells, with replication peaking at 72 hours post-transfection and decreasing after 96 hours. No replication was detected at any time point post-transfection for the defective mutant replicon. A monocistronic replicon of HCV genotype 2a was constructed and shown to be replication-proficient in human hepatocarcinoma cell lines.