RT-PCR analysis of the expression of erythroid transcription factors in EBs. Expression of mRNAs coding for ALAS-E and erythroid transcription factors GATA-1, p45, and EKLF were examined by RT-PCR. RNA samples were obtained from day 2 through day 12 EBs in culture. WT, wild-type EBs; ALAS-E(-), ALAS-E(-) EBs.