Quantification of transcripts initiated at the main start site during erythroblast differentiation.

Left panel: probe for RNase protection analysis was labeled RNA of complementary sequence to bcl-x mRNA from −930 through −412 (Probe 2, Figure 1B). Lanes labeled C contain samples of probe hybridized with yeast RNA and digested with RNase A and T1. Lanes labeled 0 hours to 48 hours indicate that the RNA used for hybridization was from mouse erythroblast cells cultured for the indicated period in the presence of EPO. Samples were digested with RNases. Lane M is marker, as described in the legend to Figure 2B. Lanes Pr2 contain undigested probe 2 samples (10 000 cpm). Right panel: probe for RNase protection analysis was labeled RNA complementary to bcl-x mRNA sequence from −754 through −412 (Probe 1, Figure 1B). Probe was hybridized with total RNA from mouse erythroblasts cultured for 36 hours and 48 hours in the presence of EPO. Hybridized samples were treated with RNase A and T1. Lane M is ΦX174 marker. Lanes Pr1 contain undigested probe 1.