Poly(A) site choice in retroelements: deja vu all over again?

The primary transcripts encoded by retroelements contain two polyadenylation [poly(A)] sites, positioned 5' and 3' of the protein-coding sequences. To ensure efficient gene expression in these systems, a mechanism must operate that suppresses use of the 5' site, enhances use of the 3' site, or both. These possibilities have been examined in a recent series of experiments that have revealed two main regulatory themes. First, maximum 3' end processing can require sequences other than core poly(A) signals, which are transcribed only before the 3' site. Second, processing is partly inhibited when the site is positioned close to the promoter. These results should serve as the basis for a more detailed understanding of how the choice of the poly(A) site is regulated in these elements.