A transcriptional insulator element, the su(Hw) binding site, protects a chromosomal DNA replication origin from position effects.
A transcriptional insulator element, the su(Hw) binding site, protects a chromosomal DNA replication origin from position effects.
复制标题
转录绝缘子元件（su(Hw) 结合位点）可保护染色体 DNA 复制起点免受位置效应的影响。
DOI：
10.1128/mcb.17.4.2202
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发表时间：
1997
影响因子：
5.3
通讯作者：
Tower,J
中科院分区：
文献类型：
--
作者：
Lu,L;Tower,J
真核染色体被组织成转录和DNA复制的活性域。转录“边界”或“绝缘体”元件已经涉及介导转录结构域的组织。然而，可能划分DNA复制活性域的DNA序列元件是未知的。su（Hw）蛋白结合位点（su（Hw）BSs）是一种有效的转录绝缘子元件，它可以阻断增强子的作用以及染色体位置的正负效应。在这里，我们报告说，侧翼苏（Hw）BS也可以创建一个染色体域允许绒毛膜基因DNA复制起点的活动。在果蝇胚胎发生过程中，通过DNA复制的重复启动，绒毛膜（蛋壳）基因位点扩增了约80倍。位于第三条染色体（ACE 3）上的顺式作用扩增控制元件是在附近的主要复制起点Ori-β启动高水平扩增所必需的。含有ACE 3和Ori-β的转基因绒毛膜基因座构建体能够扩增，但对位置效应极其敏感：21个独立插入中只有7个扩增>10倍。在构建体中包含侧翼su（Hw）BS显著地保护DNA复制免受位置效应的影响：31个插入中的31个现在扩增>10倍，并且这种保护在asu（Hw）突变体背景中降低。在su（Hw）BS的两侧扩增是相等的，表明复制叉通道不受这些位点的显著阻碍。在构建体中仅包含单个su（Hw）BS不能检测到保护绒毛膜基因DNA复制起点免受位置效应的影响。
Eukaryotic chromosomes are organized into domains of activity for both transcription and DNA replication. Transcriptional “border”, or “insulator”, elements have been implicated in mediating the organization of transcriptional domains. However, the DNA sequence elements which might demarcate domains of DNA replication activity are unknown. su(Hw) protein binding sites [su(Hw)BSs] are potent transcriptional insulator elements which can block enhancer action, as well as positive and negative chromosomal position effects. Here we report that flanking su(Hw)BSs can also create a chromosomal domain permissible for activity of the chorion gene DNA replication origin. DuringDrosophilaoogenesis the chorion (eggshell) gene loci are amplified ~80-fold through repeated initiation of DNA replication. Thecis-acting amplification control element, on the third chromosome (ACE3), is required for high levels of amplification initiating at the nearby major origin of replication, Ori-β. A transgenic chorion locus construct containing ACE3 and Ori-β was able to amplify but was extremely sensitive to position effects: only 7 of 21 independent insertions amplified >10-fold. The inclusion of flanking su(Hw)BSs in the construct dramatically protected DNA replication from position effects: 31 of 31 insertions now amplified >10-fold, and this protection was reduced in asu(Hw)mutant background. Amplification was equal on both sides of the su(Hw)BS, demonstrating that replication fork passage is not significantly impeded by these sites. Inclusion of only a single su(Hw)BS in the construct did not detectably protect the chorion gene DNA replication origin from position effects.