Viral clones, fitness increases and mutations fixed in the consensus sequences.

aLocation of mutations is assigned taking HIV-1 strain HXB-2 as a reference (Accession number #K03455). Mutations are numbered according to their position in the gene. NA: not applicable. Reversions are underlined. Amino acid substitutions are numbered in reference to the protein affected.bNucleotide substitution producing an amino acid change in two proteins.cBoth substitutions lead to the same amino acid change.dViruses passaged in 5·106 MT-4 cells are doubly underlined.