A poly(a) binding protein that is involved in promoting the extension of the poly a tails of mrna. the protein requires a minimum of ten adenosine nucleotides in order for binding to mrna. once bound it works in conjunction with cleavage and polyadenylation specificity factor to stimulate the rate of poly a synthesis by poly a polymerase. once poly-a tails reach around 250 nucleotides in length poly(a) binding protein ii no longer stimulates polyadenylation. mutations within a gcg repeat region in the gene for poly(a) binding protein ii have been shown to cause the disease muscular dystrophy, oculopharyngeal.