Regulation of the human globin gene switching mechanisum based on unusual DNA structure

人类β-珠蛋白基因座包含5个活性基因(S-、GY-、Ay-、S-和β-珠蛋白)和一个J3-珠蛋白假基因(PSIbeta-珠蛋白)，其大小超过70kb。这些基因之间的序列同源性大部分丢失，AIU和LI重复序列的插入自分离以来发生，导致核苷酸序列的完全混合。然而，当这些基因在发育和分化过程中切换表达时，它们表现出明显的协调。这需要严格控制转录机制，包括RNA聚合酶和位于42kb的启动子之间的相互作用。控制这种协调的基因座控制区位于e-珠蛋白基因上游6kb到20kb以上。因此，这些基因的表达调控为研究基因组DNA中异常DNA结构的生物学意义提供了一个很好的模型。DNA弯曲位点的周期性首次在人类epsilon-珠蛋白基因区被报道(J.Biol)。化学。269.1994)，随后在同一基因座的其他区域。基于这些结果，我们提出周期性弯曲DNA与基因组DNA的长程配位有关。在本研究中，我们用循环排列的方法在β-珠蛋白基因约70kb区域共定位了98个弯曲位点，它们之间的平均间隔约为680个碱基。它们相对于帽子位置的大部分位置在进化过程中都是保守的。在51个转折点中发现了75个潜在转折点A/A/A(A2N8A2N8A2)，48个转折点的序列显示了转折谱。这些证据表明，DNA弯曲是基因组DNA的一个基本和普遍的结构成分，并对生物现象有直接或间接的影响，如调节Golobin基因切换机制。

The human beta-globin locus contains five active genes (s-, Gy-, Ay-, S-and beta-globins) and a j3-globin pseudogene (PSIbeta-globin) in a region larger than 70 kb. The sequence homologies between these genes were mostly lost and insertions of AIu and Li repetitive sequences have occurred since their separation, resulting in a total mixture of the nucleotide sequence. However, these genes show marked coordination when they switch expression during development and differentiation. This requires strict control of the transcription machinery including RNA polymerases and the interaction between the promoters located as far as 42 kb. The locus control region that governs this coordination is located 6 kb to more than 20 kb upstream of the e-globin gene. Therefore, the regulation of expression of these genes provides a good model in which to study the biological significance of unusual DNA structure in genomic DNA.Periodicity of DNA bend sites was firstly reported in the human epsilon-globin gene region (J.Biol. Chem. 269.1994) and subsequently in other regions of the same locus. Based on the results, we proposed that periodic bent DNA are associated with Long range coordinations of genomic DNA.In this study we mapped a total of 98 bend sites in the about 70 kb region of the beta-globin locus by circular permutation assay with average interval of approximately 680 bp between them. Most of their locations relative to the cap sites were conserved during evolution. There were the 75 potentialbend core sequences A/A/A (A2N8A2N8A2) found in the 51 bend sites, 64 sequences from 48 sites showed bending profiles by oligonucleotide-based assay. These lines of evidence suggested that DNA bending is a basic and universal structural component of genomic DNA and has a direct or indirect influence on biological phenomena such as regulation of the golobin gene switching mechanism.