A nested PCR (Platinumw Taq DNA Polymerase High Fidelity, Invitrogen) was subsequently run with the primers 2584L34 (5′-TGG ATA TCT TTT GGG CCA TCC ATT CCT GGC TTT A-3′) and 2173U34 (5′-AGC TGT ACA TTT GGG GAA GAG ACA ACA ACT CCC T-3′). The nucleotides corresponding to the restriction sites used for cloning are underlined in the above sequences. 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.