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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Position-effect protection and enhancer blocking by the chicken β-globin insulator are separable activities
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Position-effect protection and enhancer blocking by the chicken β-globin insulator are separable activities

机译：鸡β-珠蛋白绝缘子的位置效应保护和增强子阻断是可分离的活动

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摘要

The 1.2-kb DNA sequence element (5'HS4) at the 5' end of the chicken β-globin locus has the two defining properties of an insulator: it prevents an "external" enhancer from acting on a promoter when placed between them ("enhancer blocking") and acts as a barrier to chromosomal position effect (CPE) when it surrounds a stably integrated reporter. We previously reported that a single CTCF-binding site in 5'HS4 is necessary and sufficient for enhancer blocking. We show here that a 250-bp "core" element from within 5'HS4 is sufficient to confer protection against silencing of transgenes caused by CPE. Further dissection of the core reveals that 5'HS4 is a compound element in which it is possible to separate enhancer blocking and barrier activities. We demonstrate that full protection against CPE is conferred by mutant 5'HS4 sequences from which the CTCF-binding site has been deleted. In contrast, mutations of four other protein binding sites within 5'HS4 result in varying reductions in the ability to protect against CPE. We find that binding sites for CTCF are neither necessary nor sufficient for protection against CPE. Comparison of the properties of 5'HS4 with those of other CTCF-binding enhancer-blocking elements suggests that CPE protection is associated with maintenance of a high level of histone acetylation near the insulator, conferred by insulator binding-proteins other than CTCF.
机译：鸡β-珠蛋白基因座5'端的1.2-kb DNA序列元件（5'HS4）具有绝缘子的两个定义特性：当位于它们之间时，它可防止“外部”增强子作用于启动子（ “增强剂阻断”），当它包围稳定整合的报道分子时，它成为染色体位置效应（CPE）的屏障。我们先前曾报道5'HS4中的单个CTCF结合位点对于增强子阻断是必要且足够的。我们在此处显示，来自5'HS4的250 bp“核心”元件足以赋予保护以防止CPE引起的转基因沉默。对核心的进一步解剖揭示了5'HS4是一种复合元素，其中可能分离出增强子的阻断和屏障活性。我们证明了由突变的5'HS4序列赋予了针对CPE的全面保护，从中删除了CTCF结合位点。相反，5'HS4内其他四个蛋白质结合位点的突变导致针对CPE的保护能力有所降低。我们发现CTCF的结合位点对于保护CPE既不是必需的也不是足够的。 5'HS4与其他CTCF结合增强剂阻滞元件的特性比较表明，CPE保护与在绝缘子附近维持高水平的组蛋白乙酰化有关，这是由绝缘子结合蛋白而非CTCF赋予的。

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