A cDNA clone from a mouse testis cDNA library was isolated by the transcomplementation method using a Schizosaccharomyces pombe meiotic mutant (sme2) that is defective in meiosis I. The cDNA clone isolated has an open reading frame encoding 302 amino acids constituting a protein with a strong similarity to mouse poly(A) binding protein II (mPABII) and bovine poly(A) binding protein II (PABII). PABII is known to bind to the growing poly(A) tail and stimulates poly(A) polymerase, which catalyzes the polymerization of the mRNA poly(A) tail. Northern blot analysis of the cDNA clone identified as mPABII revealed a single transcript of 1.2 kb. This was detectable exclusively in adult testis. Immunohistochemical analysis using a polyclonal antibody demonstrated that mPABII protein was expressed in the nucleus at specific stages from late pachytene spermatocytes to round spermatids. Genetic mapping showed the Pabp3 gene encoding mPABII to be located near position 19.5 on mouse chromosome 14. These results suggest that mPABII might be involved in specific spermatogenetic cell differentiation.