TELOMERE STRUCTURE IN DROSOPHILA

端粒是线性染色体末端的结构，它是 是基因组稳定所必需的。它们至少提供两种基本服务 功能：(1)抵消染色体末端DNA的丢失 由于DNA聚合酶不能复制染色体末端 完全，以及(2)识别不同的自然染色体末端 从断裂的染色体末端。在结构上，端粒是复杂的，有 极端端的串联重复阵列似乎对 这两个函数，一个更复杂的未知重复数组 近端功能，与这些DNA重复序列结合的蛋白质。在……里面 远端串联阵列由可转座的重复序列组成 类似于哺乳动物的线状元件和特定靶标的元件 染色体结束。果蝇中更近端的、亚端粒重复序列 和其他物种被认为与 异染色质及其附近基因的失活， 并可能有助于与其他端粒形成联系， 核基质和板层。设计了两个实验来 研究端粒功能。首先是端粒特异的转座 基因标记的元素将在#年返回到基因组 命令跟踪单个元素的换位，并剖析 基因上的转位机制。第二，亚端粒重复 从染色体末端(2L)连接到一个报告基因， 重新引入到基因组中，询问是否以及在什么情况下 在某些情况下，这种重复序列会降低基因活性。 当重复序列被上游连接到 记者在一个方向，但不是另一个方向。只删除了几个 在12个重复单位中，可以恢复基因活动。因此，该重复阵列 确实会减少转录，这可能对端粒很重要 异染色质形成。

Telomeres are structures on the ends of linear chromosomes that are required for genome stability. They serve at least two essential functions: (1) to counterbalance the loss of DNA from a chromosome end due to the inability of DNA polymerase to replicate chromosome ends completely, and (2) to identify a natural chromosome end as different from a broken chromosome end. Structurally, telomeres are complex, having a tandem repeat array at the extreme end that appears to be important for both of these functions, a more complex array of repeats of unknown function proximally, and proteins that bind to these DNA repeats. In Drosophila, the distal tandem array consists of repeats of a transposable element that resembles mammalian LINE elements and targets specifically chromosome ends. The more proximal, subtelomeric repeats in Drosophila and other species are thought to be associated with the formation of heterochromatin and the inactivation of genes placed in their vicinity, and may be instrumental in forming associations with other telomeres, the nuclear matrix and the lamina. Two experiments were designed to investigate telomere function. First the telomere-specific transposable element has been marked genetically will be returned to the genome in order to follow the transposition of a single element and to dissect the transposition mechanism genetically. Second, the subtelomeric repeats from one chromosome end (2L) have been ligated to a reporter gene and reintroduced into the genome to ask whether, and under what circumstances, this repeated sequence reduces gene activity. Transcription is reduced when the repeat is attached upstream to the reporter in one orientation, but not the other. Deletion of just a few of the 12 repeat units restores gene activity. Thus, this repeat array does reduce transcription and may be important for telomeric heterochromatin formation.