EKLF is also required for β-globin–transgene expression at the embryonic stage. RNA isolated from 10.5-day yolk sac of embryos with the various EKLF genotypes and transgenicity for the μD14 construct indicated at the top of the lanes was analyzed by RNase protection with a human β-globin–transgene probe and a mouse ^y-globin probe. The position of the protected fragments detected by each probe is indicated by the arrows to the right of the figure.