Representative autoradiograph of the primer extension analysis of MEL cell RNA, before (lanes 1, 3, 5, 7) and after erythroid differentiation induction (lanes 2, 4, 6, 8, 11, 12, 13), transfected with normal (lanes 1, 2, 11, 12, 13), β15 (lanes 3, 4), β39 (lanes 5, 6), or β127 (lanes 7, 8) β-globin genes.

Human β- and mouse α-globin specific oligonucleotides were hybridized with 10 μg murine RNA and then extended with reverse transcriptase as described in “Materials and methods.” Two hundred fifty nanograms of human reticulocyte RNA (lane 9) and 10 μg untransfected MEL cells mRNA (lane 10) were also reverse transcribed to show the positions of human β- (96 nt) and mouse α-globin (76 nt) cDNA, respectively. In addition, 1, 10, and 15 μg RNA extracted from cells transfected with the normal β-globin gene (lanes 11, 12, 13, respectively) were transcribed to show that the experiment was carried out in the presence of primer in excess. Levels of human β-globin mRNA (hβ) relative to endogenous mouse α-globin mRNA (mα) are indicated at the bottom.