We report the presence of two elements, pet and net, that are required for 
proper transcription of the duck hepatitis B virus (DHBV). These regions were 
previously identified by using plasmid clones of the virus in transient 
expression assays (M. Huang and J. Summers, J. Virol. 68:1564-1572, 1994). In 
this study, we further analyzed these regions by using in vitro-synthesized 
circular DHBV DNA monomers to mimic the authentic transcriptional template. We 
observed that pet was required for pregenome transcription from circular viral 
monomers, and in the absence of pet-dependent transcription, expression of the 
viral envelope genes was increased. We found that deletion of net in 
circularized DNA monomers led to the production of abnormally long transcripts 
due to a failure to form 3' ends during transcription. In addition, we report 
the presence of a net-like region in the mammalian hepadnavirus woodchuck 
hepatitis virus. These results are consistent with a model that net is a region 
involved in transcription termination and that in DHBV, pet is required for 
transcription complexes to read through this region during the first pass 
through net.