TABLE 3.

Classification of HIV-1 protease amino acid positions according to the distribution of substitution types at that position in patients receiving a protease inhibitor

Pattern	Description
I, conserved/invariant	All residue pairs are CC
II, polymorphic/invariant	Residue pairs are CC or NN
III, conserved/mutated	Residue pairs are CC or CN
IV, polymorphic/mutated	Residue pairs are CC, NN, CN, or NN′
V, polymorphic/revertant	Residue pairs are CC, NN, or NC
VI, polymorphic/bidirectional	Residue pairs include CN and NC