Polyadenylation of the 3-prime ends of eukaryotic mRNAs is a key event that takes place in the nucleus during maturation of mRNA. The reaction includes endoribonucleolytic cleavage of the pre-RNA at the poly(A) site that leads to synthesis of the poly(A) tail at the 3-prime end of the upstream cleavage product. The poly(A) polymerase (PAP) is required The adenosine addition reaction depends on poly(A) polymerase (PAP) activity. The testis express PAP-beta (TPAP) in the cytoplasm of spermatogenic cells. The adenosine addition function of PAP-beta plays a critical role in male germ cell production. PAP-beta-deficient transgenic mice display impaired expression of haploid-specific genes that are necessary for spermatogenesis. The intronless gene encoding human PAP-beta maps to chromosome 7p22.3.