cDNA cloning of c33-c antigen gene derived from NS3 region of Chinese HCV genome, expression in Escherichia coli and development of HCV EIA second-generation diagnostic kit.
A cDNA fragment of about 860 bp corresponding to the c33-c gene in the non-structural region 3 (NS3) of HCV genome was obtained from one plasma derived from a Chinese HCV carrier who came from Tai' an of Shandong Province, China by the application of reverse transcription (RT) and polymerase chain reaction (PCR) techniques. After the sequence of the cDNA fragment was determined and compared with the equivalent region of the HCV-I (HCV-US) and HCV-II (HCV-BK) genomes, the nucleotide/amino acid sequence homologies were found to be 79.2%/91.3%/ and 91.3%/93.9%, respectively. The prokaryotic expression vector pBV220 was employed for the overproduction of c33-c native recombinant protein in E. coli cells. The expression products were detected by enzyme-linked immunosorbent assay (ELISA) and Western blotting with antisera of chronic hepatitis C patients, and a molecular weight 31 kD of c33-c viral protein was shown to account for 14% of the total cellular soluble proteins. This product was extracted from the bacterial lysate by lysozyme, Triton X-100 and urea treatment, and purified through ion exchange chromatography. The purified c33-c protein combined with a branch peptide MAP-C-19 representing immunodominant epitopes on the nucleocapsid region of HCV genome was used to develop a Chinese HCV EIA 2nd-generation diagnostic kit for the detection of anti-HCV antibodies. Its specificity, sensitivity and reproducibility were all in keeping with the indexes of the national standard for the quality control of the HCV diagnostic kit. The agreement rate between our kit and Abbott company's HCV EIA second-generation diagnostic kit was 99.33%, and the identified rate of positive anti-HCV of our kit was 2% more than that of the Abbott company's kit.