To sequence the region containing the mouse ESG1 gene and the 3' flanking region, we subcloned a ~15 kbp XhoI-SalI fragment into the pZERO-2 vector (Invitrogen). HindIII- or EcoRI-digested fragments of this vector were then cloned into pBluescript KS(-) for sequencing. To sequence the ESG1 pseudogene and the 3' flanking region, an 8 kbp NotI/XhoI fragment was cloned into pBluescript KS(-). BamHI- or PstI- fragments of this vector were also cloned into pBluescript KS(-). To identify the sequence containing the 5' flanking regions of the ESG1 gene and the related pseudogenes, we used a TOPO walker kit (Invitrogen) with the pH34-T2L (5'-ACTAGTCGCAGCAGGGATCCAGGAATATCT-3') and pH34-L394 primers. The resulting sequence was cloned into pCR2.1 (Invitrogen). We obtained a ~6 kbp band from the NsiI-digensted library; XbaI-, SpeI-, EcoRI-, and PstI-digested fragments of this band were cloned into pBluescript KS(-) for sequencing. This fragment contained the 5' flanking region of the ESG1 gene. A ~3 kbp fragment, obtained from the SacI-digested library, was cloned into pCR2.1 for sequencing. This fragment was contained the 5' region flanking the pseudogene.