Hepatitis delta virus (HDV) is a subviral agent with a small RNA genome that is replicated in the nucleus of an infected cell. During genome replication, there is the synthesis of a complementary RNA, known as the antigenome, and also of a smaller complementary species that is polyadenylated and acts in the cytoplasm as the mRNA for the only known HDV protein, the delta antigen. We have carried out an examination of the cis- and trans-acting elements that regulate the polyadenylation process involved in the synthesis of this mRNA for the delta antigen. Our experimental approach has been to study the processing of nascent antigenomic RNA as it occurs in transfected cells via DNA-directed RNA synthesis, in the absence of genome replication. Three conclusions have been made. (i) The polyadenylation process occurs independent of the functionality of a unique self-cleavage domain located just 3' of the polyadenylation site. (ii) RNA transcripts that proceed beyond the polyadenylation site can be stabilized by the self-cleavage reaction. Thus, a single transcription initiation event can lead not only to the mRNA species but also to at least one more stable RNA species. (iii) If the nascent RNA species can fold on itself, into the so-called rodlike structure, then the presence of the delta antigen leads to a major suppression of polyadenylation. These results are incorporated into a more detailed model of the replication of the HDV genome.