Naturally occurring woodchuck hepatitis virus (WHV) deletion mutants in chronically WHV-infected woodchucks

Deletion mutants of hepatitis B virus (HBV) are often found in chronically HBV-infected patients. It has not been possible to study the significance o f such deletion mutants on liver diseases in a suitable animal model. In th is study, we characterized naturally occurring deletion mutants of woodchuc k hepatitis virus (WHV) in 11 chronically WHV-infected woodchucks. Deletion s within the WHV preS region (nt 2992-338) had a length of 72 or 84 bp and were located in the amino terminal par? of preS1. Internal deletions within the core gene (CID) had variable lengths (103 to 312 bp) and were identifi ed within the center of this gene (nt 2021-2587). Four of seven CIDs were i n-frame deletions, whereas the remaining three CIDs were out-of-frame delet ions and led to the interruption of the reading frame. Sequence analysis of cloned PCR products of CIDs showed that heterogeneous WHV deletion mutants coexisted in single woodchucks. In addition, WHV genomes with double delet ions in the preS1 and the core region could be found. We were unable to det ect the expression of truncated core proteins in transfection experiments. The CID mutations led to a marked increase of the expression of the lucifer ase gene which was fused to the start codon of WHV polymerase, probably due to the shortening of the untranslated region or the removal of AUGs preced ing the polymerase start codon. The characterization of naturally occurring WHV deletion mutants will allow us to study their biological and pathogeni c properties in the woodchuck model in the future. (C) 2000 Academic Press.