RNA analysis of wild-type and heterozygous mutant female spleens. Expression of GATA-1 from either the IE promoter (E-GATA-1) or the IT promoter (T-GATA-1) was examined after 35 cycles of amplification using 5′ primers specific for either first exon and a 3′ primer used in common in the GATA-1 third exon. Expression of neomycin phosphotransferase was also examined after 35 cycles of amplification. G6PD was used as the internal control and analyzed after 27 cycles of amplification. The numbers indicate individual animals. Lanes 1 and 2, samples isolated from wild-type spleens; lanes 3 and 4, heterozygous mutant female spleens in animals displaying mild splenomegaly; lanes 5 and 6, heterozygous mutant female spleens having marked splenomegaly. +, positive control; −, no template added; M, marker lane.