RNA-binding protein, which is involved in the polyadenylation-dependent pre-mRNA 3'-end formation and cooperates with the cleavage factor CFIA complex and the cleavage and polyadenylation factor (CPF) complex. May be involved in regulation of poly(A) site selection. Is involved in nonsense-mediated mRNA decay. Seems to bind to an RNA downstream sequence element (DSE) located 3' of a nonsense codon and may mark the transcript for decay. Interacts with NAM7. Methylated by HMT1 (PubMed:9499403, PubMed:10024178). The methylation is required for nuclear export (PubMed:9499403).