A Hepatitis B virus pregenomic RNA based minigene transcript utilizes polypyrimidine tract binding protein regulated NXF1-NXT1 nuclear export pathway

Hepatitis B virus, a pararetrovirus and member of hepadnaviridae family, harbours a partially double-stranded DNA genome that is transcribed by the host RNA polymerase II to generate an intron-containing pregenomic RNA (pgRNA). Nuclear export of pgRNA utilizing the canonical host pathways remains central to successful virus replication since it is reverse transcribed by the viral P protein within the nucleocapsid in cytoplasm. We provide direct microscopic evidence of Polypyrimidine tract binding protein (PTB) mediated inhibition of nuclear export of a pgRNA based intron-containing pre-mRNA (CPS-PRE) with quantitative RNA-FISH. We also demonstrate through RNA immunoprecipitation experiments that CPS-PRE minigene transcripts stably interact with members of NXF1-NXT1 pathway and no crosslinking with karyopherin CRM1 could be seen. Our data reinforces a novel aspect of PTB in pre-mRNA nuclear export for active retention of intron-containing transcripts and directly shows the ability of pgRNA components to interact with NXF1-NXT1 heterodimer.