[Sequencing of hepatitis B virus DNA fragment coding major HBsAg of escape mutant].

We amplificated a HBV DNA fragment coding the major HBsAg from a chronic HBsAg carrier's serum with high titer of HBsAg and anti-HBs using polymerase chain reaction (PCR). The direct sequencing of PCR products revealed a single mutation from adnosine to guanosine at the nucleotide position 532 of HBV DNA of the escape mutant. This mutation might result in an amino acid substitution from threonine to alanime at the amino acid position 126 of HBsAg. Since this amino acid is located in the first loop of the "a" determinant of HBsAg, the mutation might result in an alteration of the structural antigenicity of the "a" determinant and induce escape mutant of HBV.