NUCLEOTIDE-SEQUENCE OF A CLONED HUMAN HBV MUTANT (PDKHBV) IN DUCK HEPATOMA OF QIDONG-COUNTY

This is the first report to describe the presence of an HBV-like DNA s equence in two hepatoma and their tumor surrounding liver tissues, one precancerous and one non-malignant liver tissue of ducks collected fr om Qidong County of China. The HBV-like sequences were either in an ep isomal form of 3.2 kb or in an integrated form of various sizes, while the DHBV DNA sequences (3.0 kb) were either present or absent in thes e tissues and in different size pattern. Furthermore, there was no evi dence of cross-hybridization between HBV-like DNA sequences in duck an d DHBV DNA. A 3.2 kb HBV-like DNA sequence has been cloned from one du ck hepatoma (40 K), designated as pDKHBV. The 3218 bp full-length nucl eotide sequence of this clone has been determined, which had no appare nt homology with Duck Hepatitis B Virus (DHBV) genome, but was highly homologous to human HBV adw2 subtype (99.0%). The sequence was compose d of four open reading frames for HBV gene Pre-S/S, X, C and P respect ively. In addition to multiple sites of point mutation, one nt and two nt deletion were detected downstream the initiation codon of Pre-S1 g ene and at the 3' end of C gene respectively, thereby suggesting a fra meshift mutation in Pre-S gene and C gene. Based on these results, it was implicated that an unusual HBV variant might exist in Qidong Count y, which might have transmitted into duck through some yet unknown mec hanisms. The possibility from exogenous contamination could be thus ex cluded.