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To test the role of gene order in globin gene expression, mutant human β-globin locus yeast artificial chromosome constructs were used, each having one additional globin gene encoding a ‘marked’ transcript (ϵm, γm, or βm) integrated at different locations within the locus. When a βm-globin gene was placed between the locus control region (LCR) and the ϵ-globin gene, βm-globin expression dominated primitive and definitive erythropoiesis; only βm-globin mRNA was detected during the fetal and adult definitive stages of erythropoiesis. When an Aγm-globin gene was placed at the same location, Aγm-globin was expressed during embryonic erythropoiesis and the fetal liver stage of definitive erythropoiesis but was silenced during the adult stage. The downstream wild-type γ-globin genes were not expressed. When an Aγm-globin gene was placed between the mδ- and β-globin genes, it remained silent during embryonic erythropoiesis; only the LCR-proximal wild-type ϵ-globin gene was expressed. Placement of a βm-globin gene upstream of the Gγ-globin gene resulted in expression of βm-globin in embryonic cells and in a significant decrease in expression of the downstream wild-type βm-globin gene. These results indicate that distance from the LCR, an inherent property of spatial gene order, is a major determinant of temporal gene expression during development. [ABSTRACT FROM AUTHOR]