β-globin constructs (βΔ1,2-ENE) containing the RRV, MCDiV, ATCOPIA27_ATh-I, TWIFB1_OSa or TCUP_ZMa ENE were transiently expressed in HEK293T cells. The ENE was inserted in either forward or reverse orientation, as indicated. (A) Northern blot analysis of β-globin transcript expression using a full-size β-globin RNA probe. The same blot was probed with a mixture of Neo1, Neo2 and Neo3 oligonucleotides for NeoR mRNA expressed from the same βΔ1,2-ENE plasmid. The unmarked band above β-globin may represent either an unrelated RNA or a non-polyadenylated β-globin precursor. (B) Quantification of Northern blot signals. To control for expression and loading, the levels of β-globin transcripts were normalized to those of NeoR mRNA. The βΔ1,2 signal (lanes 1 and 10) was set to 1. The bars show the average values from three experiments ±SD.