No restoration of V1/V2 sequences. The V1/V2 domain and surrounding sequences from proviral DNA in evolution cultures were PCR amplified and analyzed by gel electrophoresis. The lengths of the amplified fragments are 460 bp (wt), 253 bp (variant 2), 304 bp (variant 3), 265 bp (variant 4), 364 bp (variant 6), 268 bp (variants 8 to 12), and 220 bp (variant 14).