Fig. 1.

AID induced frequent C-to-T mutations in nucleocapsid DNA. HepG2 cells were cotransfected with an AID or GFP expression vector and pHBV1.5 (Fig. S2A). Three days posttransfection, the nucleocapsid DNAs were purified and subjected to 3D-PCR assay (A) and DNA sequencing (B). Total RNA was also extracted for the mutation analysis in C. (A) The 3D-PCR assay was performed as described in Materials and Methods. (B) Mutation frequency of X-gene segments. The X-gene fragments were amplified using the standard PCR protocol (94 °C denaturation) and cloned into T vectors. Fifty-five clone sequences were determined. C-to-T and G-to-A mutations were significantly increased by AID expression compared with GFP expression (χ² test). (C) Mutation frequency of the X-gene fragments amplified from reverse-transcribed total RNA.