Abstract: To construct the CHO expression system of interferon-β1a (IFN-β1a) gene and to explore the expression efficacy of human IFN-β1a gene in eukaryotic cells. Methods The synthesized IFN-β1a gene was amplified and cloned into plasmid pSV2-dhfr.Cysteine 17 was mutated to serine.The constructed recombinant plasmid pSV2-dhfr-IFN-β1a was transfected to CHO-dhfr－ cells,and the monoclonal cell strains growing stably were obtained by MTX pressure screening.The genomic DNA of transfected cells was extracted;target gene was identified by PCR.The antiviral activity of IFN-β1a in transfected cells was determined by Wish cytopathic inhibition test.Results  Both PCR and restriction enzyme analysis showed that the recombinant plasmid pSV2-dhfr-IFN-β1a was constructed correctly.The IFN-β1a gene was amplified by using the genomic DNA of transfected cells as template.The expressed IFN-β1a showed high antiviral activity up to 3×105 IU·mL^-1.Conclusion A eukaryotic expression vector of IFN-β1a gene is successfully constructed,and the IFN-β1a protein with biological activity is expressed in CHO cells.

Key words: interferon &beta, 1a, eukaryotic cells, CHO cells