Fig. 1.

Hypothetic model for antisilencing regulation of alternative polyadenylation. In WT Arabidopsis, EDM2 and ASI1 bind to the intronic heterochromatin region by recognizing enriched epigenetic marks. With the assistance of an unknown factor X, the three proteins form a complex that potently masks the poly(A) signals from being recognized by the polyadenylation apparatus riding on the C-terminal domain of RNA polymerase II. Consequently, the distal poly(A) site is used. In the edm2 or asi1 mutant, absence of either EDM2 or ASI1 reduces the masking effect on the proximal poly(A) site. The result is an extensive use of the proximal site, producing shortened transcripts encoding nonfunctional proteins, leading to a silencing effect of the target gene.