The transgene includes the rabbit adult beta hemoglobin gene and a beta-2 pseudogene. in situ hybridization studies of metaphase spreads from the founder mouse chromosomes detected one transgene insertion site on Chromosome 3 and another on Chromosome 12. Southern blot analyses of G1 mice estimated 3-4 transgene copies per cell on Chr 3 and 15-25 copies on Chr 12. 3' S1 nuclease protection assays detected polyadenylated rabbit transcript in skeletal muscle (20x), brain, testis, and lung (1x), but not in erythrocytes from a G2 mouse carrying the transgene. Further 3' S1 nuclease protection studies of G2 and G3 mice carrying the transgene indicate that the rabbit transcripts in muscle have the correct 5' terminus.