科研之友
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摘要
In all hepadnaviruses, protein-primed reverse transcription of the pregenomic RNA (pgRNA) is initiated by binding of the viral polymerase, P protein, to the epsilon RNA element. Universally, epsilon consists of a lower stem and an upper stem, separated by a bulge, and an apical loop. Complex formation triggers pgRNA encapsidation and the epsilon-templated synthesis of a DNA oligonucleotide (priming) that serves to generate minus-strand DNA. In vitro systems for duck hepatitis B virus (DHBV) yielded important insights into the priming mechanism, yet their relevance in infection is largely unexplored. Moreover, additional functions encoded in the DHBV epsilon (D epsilon) sequence could affect in vivo fitness. We therefore assessed the in vivo performances of five recombinant DHBVs bearing multiple mutations in the upper D epsilon stem. Three variants with only modestly reduced in vitro replication competence established chronic infection in ducks. From one variant but not another, three adapted new variants emerged upon passaging, as demonstrated by increased relative fitness in coinfections with wild-type DHBV. All three showed enhanced priming and replication competence in vitro, and in one, DHBV e antigen (DHBeAg) production was restored. Pronounced impacts on other D epsilon functions were not detected; however, gradual, synergistic contributions to overall performance are suggested by the fact of none of the variants reaching the in vivo fitness of wild-type virus. These data shed more light on the P-D epsilon interaction, define important criteria for the design of future in vivo evolution experiments, and suggest that the upper D epsilon stem sequences provided an evolutionary playground for DHBV to optimize in vivo fitness.
- 出版日期2011-9
