Expression of globin mRNA in transgenic mice containing the β-globin distal promoter deletion construct (BGT41), distal promoter spacer construct (BGT40), and the 3′ truncation construct (BGT46). (A) S1 nuclease analysis of fetal liver RNA of 15.5 day F₀ BGT41 transgenic mice showing that the range of expression from single-copy transgenes is 26% to 79% per copy and indicating that the distal promoter is important for full expression levels within the context of the 4.0 kb LCR. (B) S1 nuclease analysis of fetal liver RNA of 15.5 day F₀ BGT40 transgenic mice showing that the range of expression from single-copy transgenes is 13% to 74% per copy and indicating that a spacer element combined with the 815 bp promoter is not sufficient to reconstitute full expression levels equivalent to those directed by the 1555 bp promoter (BGT33). (C) S1 nuclease analysis of fetal liver RNA of 15.5 day F₀ BGT46 transgenic mice showing that the range of expression from single-copy transgenes is 0% to 66% per copy and showing that 3′ sequences are required to obtain reproducible full expression levels from the 4.0 kb LCR combined with the 1555 bp promoter. Hβ, human β-globin protected probe fragment; βmaj, mouse β major protected probe fragment; Ntg, nontransgenic; μD, one copy μD14 microlocus line. {/ANNT;4224n;;35904n;0n}A {/ANNT;4224n;;76032n;0n}B {/ANNT;4224n;;133056n;0n}C