GATA-1 is a transcription factor essential for erythroid cell development, and knockdown of GATA-1 gene results in maturation arrest and transformation of erythroblasts. To clarify the mechanism that gives rise to this abnormal phenotype, genes that are aberrantly expressed in the spleen of heterozygous GATA-1 knockdown mutant mouse (referred to as GATA-1 mutant mouse) were identified by using cDNA array. One of these genes, YB-1, was found to be highly expressed in the spleen of GATA-I mutant mouse. Reporter and electrophoretic mobility shift assays revealed that the proximal GATA element in 5'-UTR region of YB-1 gene functions positively in K562 cells. Furthermore, both GATA-1 and GATA-2, which were transiently expressed in COS-7 cells, bound to this element and activated the YB-1 promoter through this element. These results suggest that YB-1 functions under the regulation of GATA factors in erythroid differentiation and aberrant expression of YB-1 gene may result in dyserythropoiesis. (C) 2003 Elsevier Science (USA). All rights reserved.