Comparisons of Amino Acid Sequences of HDAg Between Genotype II and Other Genotypes

The HDAg has the following functional domains: the cryptic RNA-binding domain (CRBD; aa 2-27); the coiled-coil structure (CCS; aa 31-52) essential for the oligomerization between the small and the large HDAg; the nuclear localization signal (aa 68-88) essential for the nuclear translocalization of HDAg; the RNA-binding domain (RBD; aa 97-146) essential for HDV RNA binding and replication; the packing signal of the large HDAg (PAS; aa 196-214) for the packaging of HDV virions [2-4]. Variations in amino acid sequences in these domains may result in differences in HDV replication or packaging. The predicted amino acid sequence of genotype II HDAg is compared with those other genotypes and shown in Table 2. Of the various domains of HDAg, the RNA-binding domain appears the most conserved within and between genotypes. The packaging signal at the carboxyl end of L-HDAg is genotype specific; it is usually highly conserved within the same genotype, but highly divergent between different genotypes. The divergence in PAS within genotype II is up to 15%, and 25%-80% between genotype II and other genotypes (Table 2). Interestingly, the amino acid sequences of some domains of a HDV genotype may be closer to a different genotype as compared to those of the same genotype, suggesting possible genetic recombination during evolution.

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