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.