The Ple143-lacZ transgene (bEMS85) was designed with the Ple143 MaxiPromoter (derived from the BAC RP11-134D15 that contains the whole NR2F2 gene plus 117kb upstream and 80kb downstream sequences) upstream of a frt-flanked beta-galactosidase (lacZ) gene, an SV40 early polyA signal, and a human HPRT complementary sequence (containing exon1, intron1, exon2, and part of intron2). This construct was targeted as a single copy knockin to the Hprtb-m3 mutant locus on the X chromosome.