Expression of pre-S1, pre-S2, and C proteins in duck hepatitis B virus infection

We have examined the expression of duck hepatitis B virus (DHBV)-associated proteins in experimentally infected ducks by an immunoblot (Western) method. The DHBV-related core protein, C protein, was identified at the position of 35,000 Da (P35). Pre-S proteins were recognized as two major bands (P37 and P28), the former representing pre-S1 and the latter pre-S2 protein. Expression of the proteins was examined in the early phase of infection in ducklings sequentially sacrificed from 6 hr postinoculation to 10 days. C protein (P35) was detected as early as 24 hr postinoculation. This timing coincided with the exponential increase of RNA transcripts and double-stranded viral DNA. Pre-S1/S2 proteins were detected at 3 days postinoculation. The early appearance of C protein suggested that the proteins were utilized for nucleic acid packaging. On the other hand, the late appearance of pre-S1/S2 proteins suggested that they were utilized in the production of virions near the end of the replication cycle.