CHROMATIN STRUCTURE AND FUNCTION

我们继续着对染色质的研究 在表达基因附近的结构。珠蛋白基因 鸡红系细胞中的家族是一个模型系统 有可能研究与调节有关的机制。 红血球期间的簇和个体家庭成员 发展。我们已经扩展了我们对功能的研究 鸡5‘端1.2 kb绝缘子DNA序列 能够阻断增强子启动子的β-珠蛋白基因座 当它们之间存在相互作用时。在早期的工作中，我们展示了 该序列中的250个碱基‘核心’片段携带一个很大的 这是增强因子阻断活动的一部分。我们现在已经展示了一个 来自核心内部的40个碱基片段本身非常活跃。我们有 发现核抽提物的成分结合到这个片段上， 结合的能力与增强子的阻断有关 活动。这使得我们能够识别中心DNA序列 活性所必需的，并部分纯化结合蛋白 那里。我们还研究了完整的1.2kb 提供位置影响保护的绝缘子元件 记者稳定地转化为细胞。我们发现绝缘体 防止表情从一行到另一行的变化， 还防止了随着时间的推移所看到的表达的缓慢消亡 在没有选择性压力的情况下。防止物种灭绝的措施是 与抗组蛋白脱乙酰化的特异性保护相关 与该基因相关的染色质。在其他研究中，我们有 显示了5‘的珠蛋白结构域边界有16kb 浓缩的染色质结构域，我们在这个结构域之外发现了一个新的 红系特异性叶酸受体基因。这种基因很可能会 在发育早期对红系细胞的增殖很重要。 它的表达模式与附近的珠蛋白不同 基因，提示绝缘体和致密染色质可能起作用 作为阻止基因交叉相互作用的屏障，可测试的 假设。

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.