Molecular cloning and sequence analysis of duck hepatitis B virus genomes of a new variant isolated from Shanghai ducks.

The genomes of duck hepatitis B virus (DHBV) from a brown duck (S5) and a white duck (S31) kept independently in Shanghai, China, were cloned and the complete nucleotide sequence of each virion DNA (DHBV-S5 and DHBV-S31) was determined. DHBV-S5 and DHBV-S31 were both 3027 bp in length and 6 bp longer than the other two DHBVs analyzed previously, DHBV16 and DHBV3. The genomes of DHBV-S5 and DHBV-S31 encoded three long overlapping open reading frames designated as P, S, and C. A possible new open reading frame was found in a complementary strand of each viral genome, as 336 bp for DHBV-S5 and 306 bp for DHBV-S31, respectively. A pair of 3-bp insertions were found in the overlapping region of pre-S2 and P and so two amino acids were inserted in this region in DHBV-S5 and DHBV-S31. The nucleotide sequence variation between DHBV-S5 and DHBV-S31 (4.9%) was similar to that between DHBV16 and DHBV3 (5.6%), and less than the variations between either of these Shanghai clones and DHBV16 or DHBV3 (9.5-10.4%). The amino acid sequence was also conserved in the two Shanghai clones but showed group difference from DHBV16 or DHBV3. Thus these two independent Shanghai clones of DHBV showed geographical characteristics of genomic structure.