Impaired expression of heme biosynthetic enzymes inGATA-1.05 mutant. The expression of mRNAs for four heme biosynthetic pathway enzymes were examined in the wild-type andGATA-1.05 mutant hematopoietic cells. Amounts of the cDNAs used for the RT-PCR analyses were adjusted by dilution to produce equal amount of HPRT amplicon. The expression of two β-type globin mRNAs was also examined. ɛy-globin mRNA is expressed only in primitive erythroid cells, whereas β-major globin mRNA is expressed in definitive erythroid cells.