GATA-1, SCL, and Ldb-1 co-occupy active genes in megakaryocytes and mast cells. ChIP analysis using GATA-1, SCL, Ldb-1, or isotype-matched control antibodies in megakaryocytic L8057 cells (A) and primary bone marrow–derived mast cells (B). The −3-kb region upstream of αIIb served as negative control. The data shown are the averages of 3 or more independent experiments in panel A and 2 independent experiments in panel B. Error bars represent SDs.