Mouse and human +9.5 enhancer alleles. The wild-type mouse +9.5 configuration is depicted, with 3 mutant mouse alleles below. Ets-only and GATA-only mutants fail to support developmental hematopoiesis and are both embryonic lethal. The Ets motif point mutant that models the human single-nucleotide mutation exhibits largely normal developmental hematopoiesis yet is incompetent to support regeneration of the hematopoietic system postmyeloablation. Human alleles identified in patients with GATA2-deficiency syndrome are depicted. Black arrow extending from +9.5 to promoter, transcriptional activation; gray arrow, partial activation; absence of an arrow, severely attenuated enhancer activity. E, E-box-binding protein.