Identification of a Unique Splicing Regulatory Cluster in Hepatitis B Virus Pregenomic RNA

HBV particles with genome derived from spliced mRNAs accumulate in patients with virus-derived severe liver necrosis and fibrosis. We investigated the role of an intronic element (intronic splicing silencer-long, ISS(L)) on splicing of HBV minigene transcripts. Removal of the entire ISS(L) showed two-fold increase in splicing while shorter deletions within ISS(L) indicated isolated clusters of activator and repressor domains. Activator domains stimulated splicing in presence of PRE, a long HBV 3' exon and even when present in a heterologous context. Mutations in the repressor domain unexpectedly augmented repression. The role of this intronic splicing regulatory element could be important for HBV pathogenesis.