 The binding protein is also involved in mRNA precursors by helping polyadenylate polymerase add the poly(A) nucleotide tail to the pre-mRNA before translation.The nuclear isoform selectively binds to around 50 nucleotides and stimulates the activity of polyadenylate polymerase by increasing its affinity towards RNA.Poly(A)-binding protein is also present during stages of mRNA metabolism including nonsense-mediated decay and nucleocytoplasmic trafficking.