Igarashi K, Itoh K, Motohashi H, Hayashi N, Matuzaki Y, Nakauchi H, Nishizawa M, Yamamoto M
Department of Biochemistry, Tohoku University School of Medicine, Sendai, Japan.
J Biol Chem. 1995 Mar 31;270(13):7615-24. doi: 10.1074/jbc.270.13.7615.
Transcription factor NF-E2 is believed to be crucial for the regulation of erythroid-specific gene transcription. The three small Maf family proteins (MafF, MafG, and MafK), which are closely related to c-Maf proto-oncoprotein, constitute half of NF-E2 activity by virtue of forming heterodimers with the large, tissue-restricted subunit of NF-E2 (p45). We isolated cDNA clones encoding the murine small Maf family protein MafK and characterized the structure, activity, and expression profile of MafK mRNA. Functional analyses demonstrate that MafK binds to consensus NF-E2 sites in the absence of p45 in vitro and represses transcription of NF-E2 site-dependent reporter genes in transient transfection assays, while p45 introduced into cells alone does not effectively bind to DNA and does not affect transcription. In the presence of p45, MafK confers site-specific DNA binding activity to p45, and p45 in turn mediates transcriptional activation with its amino-terminal proline-rich domain. mRNA for MafK is expressed in fractions enriched for hematopoietic stem cells as well as erythroid cells, suggesting that MafK plays an important regulatory role in hematopoiesis.
转录因子NF-E2被认为对红系特异性基因转录的调控至关重要。三种小Maf家族蛋白（MafF、MafG和MafK）与c-Maf原癌蛋白密切相关，它们通过与NF-E2的大型组织限制性亚基（p45）形成异二聚体，构成了NF-E2活性的一半。我们分离了编码小鼠小Maf家族蛋白MafK的cDNA克隆，并对MafK mRNA的结构、活性和表达谱进行了表征。功能分析表明，MafK在体外不存在p45的情况下与共有NF-E2位点结合，并在瞬时转染实验中抑制NF-E2位点依赖性报告基因的转录，而单独导入细胞的p45不能有效结合DNA且不影响转录。在存在p45的情况下，MafK赋予p45位点特异性DNA结合活性，而p45反过来通过其富含脯氨酸的氨基末端结构域介导转录激活。MafK的mRNA在富含造血干细胞以及红系细胞的组分中表达，这表明MafK在造血过程中发挥重要的调控作用。
