CONTROL OF DEVELOPMENTAL GENE EXPRESSION--CHROMATIN STRUCTURE OF ACTIVE GENES

一个非常简单的模型系统，细胞黏液霉菌，网柄菌属 Discoideum，正被用来研究控制 发育基因在正常分化过程中的激活。因为. 基本监管机制的相似性，这一制度代表了一种 有吸引力的动物研究替代方案。在成长期和早期 聚集期的网盘基细胞表达其单个细胞的50%-55% 复制基因组作为信使核糖核酸和核糖核酸。另外26%的单拷贝基因组 仅在发展的后期阶段才表现出来。发起 在基因组的晚期转录需要细胞-细胞 互动和露营。因为这么高的比例这个小 真核生物的基因组是结构性转录的或发育的 它提供了一个独特的机会来研究结构 转录活性基因在染色质中的组织。我们的结果 表明无论是体质表达还是发育性表达 可诱导基因位于染色质中对DNase I敏感的活性结构中 不管发育诱导基因是不是 抄写的。相比之下，微球菌核酸酶被用来鉴定一种 实际上处于这个过程中的基因所特有的结构组织 被转录的可能性。该组织的属性已用于 解析特定来源于活性转录的寡核小体 并确定它们的蛋白质组成。核小体来自 转录活性基因缺乏组蛋白H1，而来自 不活跃的基因含有H1。

A very simple model system, the cellular slime mold, Dictyostelium discoideum, is being used to study the mechanisms which control developmental gene activation during normal differentiation. Because of the similarity of basic regulatory mechanisms, this system represents an attractive alternative to animal research. During growth and the early stages of aggregation Dictyostelium cells express 50-55% of their single copy genome as mRNA and HnRNA. An additional 26% of the single copy genome is expressed only during the late stages of development. Initiation of transcription on the late portion of the genome requires cell-cell interaction and cAMP. Because such a high proportion of this small eukaryotic genome is either constitutively transcribed or developmentally induced, it offers a unique opportunity to study the structural organization in chromatin of transcriptionally active genes. Our results indicate that both the constitutively expressed and developmentally inducible genes are in a DNase I-sensitive, active structure in chromatin regardless of whether the developmentally inducible genes are being transcribed. By contrast, micrococcal nuclease has been used to identify a structural organization unique to genes which are actually in the process of being transcribed. Properties of this organization have been used to resolve oligonucleosomes specifically derived from actively transcribed genes and to determine their protein composition. Nucleosomes from transcriptionally active genes are devoid of histone H1, while those from inactive genes contain H1.