The surface (S) genes of 12 hepatitis B viruses (HBVs) encoding nine different serotypes of hepatitis B surface antigen (HBsAg) were amplified by the polymerase chain reaction and sequenced. These represented the eight strains of HBV, P1 to P8, defined at an international workshop on HBsAg subtypes in Paris in 1975, and the subtype. The S genes from additional HBV strains, one , one and one , of sub-Saharan African origin, were also sequenced. The relationship of these 12 new S gene sequences to those of the 20 published previously was investigated by constructing a phylogenetic tree, which confirmed a previous classification into four groups, designated A to D, based on 18 complete HBV genomes. When relating our sequenced S genes to these genomic groups, of African origin and P6 (2) were both allocated to group A, the reference P1 ( of Vietnamese origin) was allocated to group B, P5 (), P8 () and were all related to group C, and P2 (2) and P3 (3) could both be allocated to group D. Interestingly, the S genes of serotype viruses, i.e. P4 (4) and P7 ( ), differed by 4% or more from both previous groups and from each other, suggesting their classification into two new groups, for which the designations E and F are proposed. Genomes specifying were also found in groups A and B; previously sequenced genomes specifying the subtype have all been confined to group D. There were indications that the epitope for subdeterminants of resided at amino acid positions 125 to 127. Thus, at positions 125 and 127, and had T and P residues, respectively, whereas M and T residues were at the corresponding positions of . Both and had L at residue 127, and all strains expressing , apart from P5, had an I instead of a T residue at position 126.


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