The replication of retroviruses and pararetroviruses (such as caulimo- and hepadnaviruses) involves the production of terminally redundant genomic-length RNA. The sequence repeated at both ends of the RNA (the R region) contains a polyadenylation signal, and for production of full-length RNA the version of this at the 5' end of the template must be bypassed by RNA polymerase, but the version at the 3' end must be recognized. This implies that the position of the polyadenylation signal determines its efficiency, and we report here experiments aimed at investigating the basis of this phenomenon. Our results with cauliflower mosaic virus suggest that proximity to the transcription initiation site inhibits messenger RNA 3'-end processing directed by polyadenylation signals.