Yeast three-hybrid screen cDNA library construction. Total RNA from rat testis (Lewis) was isolated with Trizol reagent (Sigma) and mRNA was purified on Oligo(dT) cellulose columns (Molecular Research Center). Hundred microgram of mRNA was used for cDNA synthesis using the Gibco BRL cDNA Synthesis System, according to the manufacturer's instructions. EcoRI adapters (Gibco BRL) were ligated to the cDNA, followed by insertion into the EcoRI site of the pYESTrp1 vector (Invitrogen). The generated cDNA library contained roughly 1.5 Â 10 6 clones.