Fig. 8. Exon 6D sequence alignments. The exon 6D splicing regulatory region has been aligned in divergent HIV-1 isolates of the B subtype (Myers et al., 1996). Lower-case bases indicate aligned nucleotides, upper-case bases indicate misaligned nucleotides, dots indicate gaps. Shaded areas indicate the elements of the exon 6D splicing regulatory region (U-to-C mutation, GGGA sequence and polypurine element, respectively, from left to right). The region coding for the variable V1 loop is also indicated. The HXB2 isolate, from which the exon 6D sequence used in this study was derived, is underlined.