Chromatin Structure in Drosophila Telomeres

插入端粒中的亚末端端粒相关序列（TAS）和末端反转录转座子阵列之间或TAS内的转基因被抑制和多样化。这种杂色，被称为端粒位置效应（TPE），似乎是由于抑制诱导TAS和激活启动转录的反转录转座子的相互作用。端粒转基因因此提供了这种相互作用的测定。这些转基因提供了一种手段来研究控制HeT-A转录和转座，从而端粒延长。通过这些转基因的至少一些转录起始于末端阵列中的上游反转录转座子。以前的研究已经确定了TPE发生的遗传条件和抑制TPE的条件。本项目的目的是确定染色质结构的变化相关的活动和抑制TPE。通过微球菌核酸酶和DNA酶1消化监测核小体阵列，并通过染色质免疫沉淀法测定蛋白质含量。迄今为止，TAS和反转录转座子阵列之间的核小体阵列没有差异，但这些DNA结构域之间的蛋白质含量不同。TAS优先结合与异染色质相关的染色质蛋白，而反转录转座子优先结合与活性染色质相关的蛋白，尽管我们已经发现异染色质蛋白HP1与反转录转座子阵列中的转基因标记物相关，并且HP1的水平与转录活性水平相关。 在染色体2L顶端的这些TAS阵列之一的缺陷或缺失增加了所有其他测量的端粒处的转基因活性。通过扩展，我们推断，逆转录转座子转录增加的端粒缩短的存在下，这将是一种机制，维持一个稳定状态的端粒长度。

A transgene inserted in the telomere between the subterminal telomere associated sequence (TAS) and the terminal retrotransposon array, or within TAS, is repressed and variegates. This variegation, termed telomeric position effect (TPE), appears to be due to an interaction of repression induced by TAS and activation initiated by transcription of the retrotransposons. A telomeric transgene thus provides an assay for this interaction. These transgenes provide a means to investigate the control of HeT-A transcription and transposition, and thus telomere elongation. At least some of the transcription through these transgenes initiates in the upstream retrotransposon in the terminal array. Previous studies have identified genetic conditions in which TPE occurs and conditions in which it is suppressed. The purpose of this project is to identify changes in chromatin structure associated active and suppressed TPE. Nucleosome arrays are monitored by Micrococcal nuclease and DNase 1 digestion, and protein content assayed by chromatin immunoprecipitation. To date, no differences in the nucleosome array have been identified between TAS and the retrotransposon array, but protein content varies between these DNA domains. TAS preferentially binds chromatin proteins associated with heterochromatin, while the retrotransposons preferentially bind proteins associated with active chromatin, although we have found that the heterochromatin protein, HP1, associates with transgenic markers in the retrotransposon array, and the level of HP1 correlates with the level of transcriptional activity. Defects in, or deletions of, one of these TAS arrays at the tip of chromosome 2L increase transgene activity at all other measured telomeres. By extension we infer that retrotransposon transcription is increased in the presence of shortened telomere, which would be a mechanism for maintaining a steady-state telomere length.