RNA splicing possibilities in the HBV genome. Splice patterns in HBV pregenomic RNA are predicted by NetGene2. Genome organization is presented as functional domains in pgRNA decorated with transcription factor binding sites (upper two panels) from terminal repeat (tr) to polyadenylation sequence (pA) (bottom line). PRE indicates the position of the Posttranscriptional Regulatory Element. Different modes of splicing are numbered and referred to in the text.