Bach2 is a B-cell-and neuron-specific transcription repressor that forms heterodimers with theEukaryotic genes are most often regulated by the simultaneous, synergistic activity of several transcription factors. Protein-protein interactions play important roles in synergistic activity among these factors. In this respect, the BTB/POZ domain (2, 4, 43) may be of particular interest because of its recurrent presence in transcription factors and its activity with regard to directing specific interactions. The genome project of Caenorhabditis elegans revealed that worms possess more than 100 genes that code for BTB/POZ domain proteins. Thus the BTB/POZ domain constitutes one of the largest families of protein domains in multicellular organisms (10). Interestingly, transcription factors encoding this domain are thought to play a variety of structural and organizational roles (1,2,4,13,21,34,35). For example, the Drosophila GAGA factor is involved in chromatin remodeling and in mediating enhancer-promoter interactions (34). Alterations of the PLZF and BCL6 genes, both encoding BTB/POZ factors, are associated with oncogenesis (9, 41). BTB/POZ domains appear to direct specific protein-protein interactions. However, the exact significance of such interactions in transcription regulation remains unclear.The mammalian transcription factors Bach1 and Bach2 (36) belong to the CNC-related bZip factors that include the hematopoietic factors NF-E2 p45 (3), Nrf1 (6,7,28), Nrf2 (18,31), and Nrf3 (24). Among these factors, Bach1 and Bach2 are unique in that they each possess a BTB/POZ domain. The CNC-related factors form heterodimers with the Maf-related factors through the leucine zippers and bind to the DNA sequence motif called MARE, which contains an AP-1 binding sequence. MARE is found in regulatory regions of various genes like ␤-globin genes, immunoglobulin heavy-chain genes, antioxidant response genes (e.g., GST genes), and crystallin genes (20). These observations suggest that transcription factors binding to the MARE may play important roles in a variety of vertebrate cell types and that only very few of the actual target genes of the CNC family have been identified.Among the CNC-related factors, Bach1 and Bach2 function as transcription repressors. In B cells, Bach2 represses the immunoglobulin heavy-chain 3Ј enhancer, or LCR, perhaps through binding to the corepressor SMRT (32). Since Bach2 possesses the BTB/POZ domain in the N terminus, it may regulate gene expression by interacting with other factors through the BTB/POZ domain. In this study, we identified a new BTB/POZ domain factor, MAZR, which associates with Bach2 through the BTB/POZ domain. MAZR stimulated transcription despite of its lack of any apparent transcription activation domain. Rather, BTB/POZ-mediated oligomer formation was important for transcriptional activity, suggesting that MAZR might be not a typical transactivator but an architectural transcription factor like Drosophila GAGA factor (21). Together with previous observations, our results suggest...

Transcription factor GATA-2 is essential for the proper function of hematopoietic stem cells and progenitors. Two first exons/promoters have been found in the mouse GATA-2 gene, and a distal IS promoter shows activity specific to hematopoietic progenitors and neural tissues. To ascertain whether the two-promoter system is also utilized in the human GATA-2 gene, we isolated and analyzed a P1 phage clone containing this gene. The nucleotide sequence of the human GATA-2 gene 5' flanking region was determined over 10 kbp, and a human IS exon was identified in the locus through sequence comparison analysis with that of the mouse GATA-2 IS exon. RNA blotting and reverse-transcribed PCR analyses identified a transcript that starts from the IS exon in human leukemia-derived cell lines. The IS-originated transcript was also identified in CD34-positive bone marrow and cord blood mononuclear cells, which are recognized as clinically important hematopoietic stem cell-enriched fractions. Phylogenic comparison of the human and mouse GATA-2 gene sequences revealed several regions in the locus that exhibit high sequence similarity. These results demonstrate that the GATA-2 gene regulatory machinery is conserved among vertebrates. The fact that the human IS promoter is active in the hematopoietic stem cell/progenitor fraction may be an important clue for the design of a vector system that can specifically express various genes in hematopoietic stem cells and progenitors.

We previously reported that the mouse GATA-2 gene is regulated by two alternative promoters (Minegishi et al, J Biol Chem, 273:3625, 1998). Although the more proximal IG (general) promoter is active in almost all GATA-2–expressing cells, the distal IS (specific) promoter activity was selectively detected in hematopoietic tissues but not in other mesodermal tissues. We report here in vivo analysis of the GATA-2 locus and its regulatory characteristics in hematopoietic tissues of transgenic mice. Transgenes containing 6 or 7 kbp of sequence flanking the 5′ end of the IS first exon direct expression of β-galactosidase or green fluorescent protein (GFP) reporter genes specifically to the para-aortic splanchnopleura, aorta-gonads, and mesonephros (AGM) region, and in the neural tissues. In situ hybridization analysis showed that reporter gene expression specifically recapitulates the endogenous expression profile of GATA-2 in these tissues. The flk-1, CD34, c-kit, and CD45 antigens were identified in the GFP-positive cells from the AGM region and fetal liver, indicating that GATA-2 is expressed in immature hematopoietic cells. Deletion of 3.5 kbp from the 5′ end of the 6.0 kbp IS promoter construct, including one of the DNase I hypersensitive sites, completely abolished hematopoietic expression. These experiments describe an early developmental GATA-2 hematopoietic enhancer located between 6.0 and 2.5 kbp 5′ to the IS exon.