PCR-amplified fragments of HIV-1 protease from infected subjects were digested with the restriction enzymes BsrGI and EcoRV, and the resulting 421 bp fragment was then ligated into a BsrGI/EcoRV pre-digested pcDNA3_GFPDPR vector. After transformation of competent Escherichia coli cells, population protease-recombinant plasmids were obtained and their protease genotypes verified by DNA sequencing.