Analysis of RT-PCR products of full-length 4.1R erythroblast mRNA. Total RNA was purified from well-hemoglobinized erythroblasts, transcribed into cDNA, and amplified by RT-PCR using primer sets to amplify full-length coding domains from two populations of 4.1R cDNA: those that contained AUG-1 and those that deleted AUG-1 (A). Erythroblast cDNA amplified with exon 2′ (sense) and exon 21 (antisense) primers gave a product of ∼2.5 kb when analyzed on a 0.7% agarose gel (B, lane 1). Eythroblast cDNA amplified with exon 2 (sense) and exon 21 (antisense) primers also gave a product of ∼2.5 kb (B, lane 2). These amplification products were consistent with the predicted sizes of protein 4.1R cDNAs either containing or deleting AUG-1. By Southern blot analysis of amplified cDNA products, both RT-PCR products hybridized with 80-kD full-length 4.1R DNA, identifying them as 4.1R (C).