Abstract

Duck hepatitis B virus (DHBV) appears to lack a homologue of the X protein found in mammalian hepadnaviruses. By replacing stop codons in the corresponding region of the DHBV genome, a hypothetical protein which closely matches the hydrophilicity profile of X proteins can be predicted, despite limited sequence homology. We conclude that a full-length X protein was once a common feature of the hepadnaviruses, conserved in structure but not sequence.