Table 4

Comparison of HIV-1 and HIV-2 envelope (partial C2 to gp41 ectodomain) diversity, amino acid entropy, and sites under positive and negative selective pressure

ParameterHIV-2HIV-1P value
Mean pairwise genetic distance (no. of substitutions/site)0.183 (0.181–0.185)a0.148 (0.146–0.151)<0.0001
Mean Shannon's entropy0.255 (0.207–0.303)0.347 (0.292–0.402)0.01
Selection analysis (from a total of 277 codons)b
    SLAC
        No. of positively selected sites519<0.0001
        No. of negatively selected sites12253
    FEL
        No. of positively selected sites1122<0.0001
        No. of negatively selected sites14079
    REL
        No. of positively selected sites2151<0.0001
        No. of negatively selected sites195143
  • a Data in parentheses are 95% confidence intervals.

  • b Codons with a P value of <0.05 (SLAC and FEL) or a Bayes factor of >50 (REL) considered significant.