EFFECT OF FRAMESHIFT MUTATION IN THE PRE-C REGION OF HEPATITIS-B VIRUS ON THE X-GENE AND C-GENE

We have previously cloned a mutant hepatitis B virus (HBV) genome whic h had one thymidine addition in the pre-C region resulting in a frames hift mutation in the pre-C region and fusion of the X and C genes. We constructed plasmids containing serially deleted and/or back-mutated ( authentic) pre-C regions to study the effect of the frameshift mutatio n. COS cells transfected with plasmids containing the frameshifted pre -C region produced a 21K C protein (P21c) but not a 22K partially proc essed pre-C protein (P22). On the other hand, COS cells transfected wi th plasmids containing the back-mutated pre-C region produced P22. Thi s result was also observed in HepG2-K8 cells producing the mutant HBV particles. Therefore, the pre-C region of HBV is likely to be non-esse ntial for virus replication. COS cells transfected with the plasmid co ntaining a fused X-C open reading frame (ORF) produced a 40K X-C fusio n protein. This X-C fusion protein exerted transcriptional trans-activ ation. These results suggest that the mutant HBV has a C gene with a d efective pre-C region and a fused X-C ORF, and hence cannot synthesize 16K HBeAg (P16e).