B-cell factor 1 is required for optimal expression of the DRA promoter in B cells.

The X box in the DRA promoter of the human histocompatibility complex is required for expression of the DRA gene in B cells. We show that a B-cell factor binds to a sequence that is clearly distinguishable from binding sites for the previously described X box binding nuclear proteins RF-X, NF-X, NF-Xc, NF-S, hXBP, and AP-1. Mutations in the DRA X box that disrupt the binding of this factor result in a lower level of gene expression, as does the presence of Id (a trans-dominant regulatory protein that negatively regulates helix-loop-helix proteins). Furthermore, this factor is recognized by antibodies directed against the helix-loop-helix protein A1, a mouse homolog of the immunoglobulin enhancer binding proteins E12/E47, and it binds to sequences in other genes that were previously shown to bind these proteins. By these criteria, this factor is BCF-1.     

儿童孤独症相关基因NRXN1β启动子功能分析

Neurexins是神经特异性突触蛋白,Neurexin1β结构的异常与孤独症密切相关。为分析孤独症相关基因NRXN1β最小启动子和调节基因转录的功能元件,本文构建了含NRXN1β基因上游调控区不同区域的荧光素酶报告基因质粒,转染HEK293细胞后,利用检测双荧光素酶报告基因的转录活性以确定NRXN1β基因最小启动子区,进而筛选出相应的显著增强或抑制报告基因活性的功能区;同时,为鉴定顺式作用元件,利用基因定点突变技术对基因功能区内和临近DNA序列进行连续的碱基突变;最后,采用转录因子预测工具对启动子功能区内的转录调控元件进行分析。结果首次发现NRXN1β最小启动子区位于-88~+156 bp,-88~-73 bp和+156~+149 bp可增强启动子活性,+229~+419 bp可抑制启动子活性,且-84~-63 bp为能够显著性增强启动子活性的顺式作用元件,该区域可能存在DBP(Albumin D-site-binding protein,DBP)和ABF1(Autonomously replicating sequence-binding factor 1,ABF1)两个转录因子结合位点。     

Inhibition of muscle-specific gene expression by Id3: requirement of the C-terminal region of the protein for stable expression and function.

We have examined the role of an Id-like protein, Id3 (also known as HLH462), in the regulation of muscle-specific gene expression. Id proteins are believed to block expression of muscle-specific genes by preventing the dimerization between ubiquitous bHLH proteins (E proteins) and myogenic bHLH proteins such as MyoD. Consistent with its putative role as an inhibitor of differentiation, Id3 mRNA was detected in proliferating skeletal muscle cells, was further induced by basic fibroblast growth factor (bFGF) and was down-regulated in differentiated muscle cultures. Overexpression of Id3 efficiently inhibited the MyoD-mediated activation of the muscle-specific creatine kinase (MCK) reporter gene. Deletion analysis indicated that the C-terminal 15 amino acids of Id3 are critical for the full inhibitory activity while deleting up to 42 residues from the C-terminus of the related protein, Id2, did not affect its ability to inhibit the MCK reporter gene. Chimeric protein containing the N-terminal region of Id3 and the C-terminus of Id2 was also non-functional in transfected cells. In contrast, wild-type Id3, the C-terminal mutants, and the Id3/Id2 chimera could all interact with the E-protein E47in vitro. Additional studies indicated that truncation of the Id3 C-terminus might have adversely affected the expression level of the mutant proteins but the Id3/Id2 chimera was stably expressed. Taken together, our results revealed a more complex requirement for the expression and proper function of the Id family proteins than was hitherto expected.     

细胞分化抑制因子（Id）研究进展

Id分子(分化抑制因子/DNA结合抑制因子)是一组对碱性螺旋-环-螺旋（bHLH）转录因子活性起负调节作用的转录因子,可抑制细胞分化,促进细胞增殖.哺乳类动物细胞含Id1～Id4 4种Id因子.该分子参与细胞周期调控过程,包括细胞发育、成熟、生长、分化以及死亡等.自1990年发现Id分子以来,有关该分子在基因表达调控、细胞增殖、分化、衰老和肿瘤发生等方面进行了广泛而深入的研究. Id蛋白已成为研究细胞生命过程以及探寻治疗人类疾病有效靶向药物的一类重要分子.