CHROMATIN STRUCTURE AND FUNCTION

我们继续研究染色质 表达基因附近的结构。所述球蛋白基因 鸡红系细胞中的一个家族作为模型系统，其中 有可能研究与调节相关的机制， 在红系期间家族的簇和个体成员 发展我们已经扩展了我们的研究的功能， 1.2在鸡的5'端的kb绝缘子DNA序列 β-珠蛋白基因座，其能够阻断增强子-启动子 当他们之间的互动。在早期的工作中，我们展示了 该序列中的一个250 bp的“核心”片段携带一个大的 部分增强子阻断活性。我们现在已经证明， 来自核心内的40 bp片段本身非常活跃。我们有 发现核提取物的成分与该片段结合， 并且结合的能力与增强子阻断相关 活动这使我们能够确定中央DNA序列 活性所必需的，并部分纯化结合蛋白质， 那里我们还研究了完整的1.2kb 绝缘体元件，其提供保护以防止位置效应， 稳定转化到细胞中的报告基因。我们发现绝缘体 防止表达从一行到另一行的变化， 也可以防止表达随着时间的推移而缓慢消失， 在没有选择性压力的情况下。防止灭绝是 与对组蛋白去乙酰化的特异性保护有关， 与基因相关的染色质。在其他研究中， 显示珠蛋白结构域边界5 ′有一个16 kb的 浓缩的染色质结构域，除此之外，我们发现了一个新的 红细胞特异性叶酸受体基因。该基因很可能 对发育早期的红系细胞增殖很重要。 它的表达模式与邻近的珠蛋白不同 基因，这表明绝缘子和致密染色质可能起作用， 作为基因交叉作用的屏障， 假说.

We have continued our studies of chromatin structure in the neighborhood of expressed genes. The globin gene family in chicken erythroid cells serves as a model system in which it is possible to study the mechanisms associated with regulation of the cluster and individual members of the family during erythroid development. We have extended our studies of the function of the 1.2 kb insulator DNA sequence at the 5' end of the chicken beta-globin locus, which is capable of blocking enhancer-promoter interaction when it lies between them. In earlier work we showed that a 250 bp 'core' fragment within this sequence carries a large part of the enhancer blocking activity. We have now shown that a 40 bp fragment from within the core is itself very active. We have found that components of nuclear extracts bind to this fragment, and that the ability to bind is correlated with enhancer blocking activity. This has allowed us to identify the central DNA sequence necessary for activity, and to purify partially the protein that binds there. We have also investigated the ability of the full 1.2 kb insulator element to confer protection against position effects in reporters stably transformed into cells. We find that the insulator protects against variability of expression from one line to another, and also prevents the slow extinction of expression over time seen in the absence of selective pressure. Protection against extinction is associated with specific protection against histone deacetylation in the chromatin associated with the gene. In other studies we have shown that 5' of the globin domain boundary there is a 16 kb condensed chromatin domain, beyond which we have found a new gene for an erythroid-specific folate receptor. The gene is likely to be important for erythroid cell proliferation early in development. Its pattern of expression is different from that of the nearby globin genes, suggesting that the insulator and compact chromatin may act as a barrier against cross-interaction of the genes, a testable hypothesis.