Analysis of PI susceptibility and viral replicative capacity of NC/p1 cleavage site mutants. (A) Sequences of the NC/p1 cleavage site mutants used in this study. Nucleotide changes and amino acid changes (bold) as compared to the wild-type virus HXB2 are indicated. (B) Analysis of drug susceptibility of the NC/p1 cleavage site mutants to RO033-4649, lopinavir (LPV), tipranavir (TPV) and ritonavir (RTV). Indicated are the fold changes in EC50 compared to wild-type. (C) Viral replication curves of the different NC/p1 cleavage site mutants (HXB2436E+437T, HXB2437T, HXB2437V and HXB2431V) as compared to the wild-type HXB2. Error bars indicate the standard error of the mean.