A novel nucleotide insertion in S gene of hepatitis B virus in a chronic carrier

Abstract

Hepatitis B virus DNA was extracted from serum of a chronic carrier and polymerase chain reaction was performed on S gene. Direct sequencing showed a variant HBsAg with additional 4-amino acid insertion, and clone sequencing confirmed the mixture of variant HBsAg and wildtype HBsAg. Of 16 clones with 12-nucleotide insertion, 15 clones had identical AGAACAACACAA insertion between nucleotide 494 and nucleotide 495, and one clone had GGAACAACTCAA insertion in the same position plus 3-nucleotide deletion from nucleotide 491 to nucleotide 493. S114T, C121Y, T126S/A, Q129K, G130R, T131N, M133T, G145R, N146D substitution and premature stop codon were also found in those clones. However, the origin of HBV with 4-amino acid insertion in HBsAg was unclear.

Figure 1

Alignment of nucleotide sequences in the HBs1 region of 06A26 PCR amplicon and clones with genotype A-H reference isolates. Homologous nucleotides were indicated with dots, deleted nucleotides with dashes. Heterologous nucleotides are specified. Inserted nucleotides were indicated with grey boxes.

Figure 2

Alignment deduced amino acid sequences in MHR(aa99-aa169) of 20 clones with consensus sequence from published Chinese isolates with genotype B/subtype adw2(GenBank accession number AB033554, AF100309, D00329, AF397207, EU305547, EU589335 and GU145102). One-letter code was used for amino acid in consensus sequence, homologous amino acids were indicated with dots, deleted amino acid with dash, and premature stop codon with asterisk. Heterologous amino acids were specified. Inserted amino acids were indicated with grey boxes.