Telomere Structure In Drosophila

端粒是染色体末端的核蛋白结构，其需要完全复制线性DNA并将天然染色体末端与双链染色体断裂区分开来以进行DNA修复。在果蝇中，染色体末端通过三种逆转录转座子HeT-A、TAHRE和TART的靶向转座以及端粒之间的基因转换来维持。在野生型中，转座和基因转换足以平衡由于不完全DNA复制而导致的逐渐染色体缩短。已知突变会显著增加或减少逆转录转座子添加到染色体末端的频率，这表明该过程受遗传控制。我们已经确定了一个增加末端基因转换频率的突变，并正在使用位置信息克隆基因。 插入端粒的转基因会受到抑制，称为端粒位置效应，TPE。TPE存在于各种物种中，包括酵母、昆虫和人类。在果蝇中，在近末端端粒相关序列（TAS）中或TAS和末端反转录转座子阵列之间的转基因被抑制和多样化。这种杂色似乎是由于抑制诱导TAS和激活启动HeT-A转录的相互作用。端粒转基因因此提供了这种相互作用的测定。这些转基因可能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。插入到TAS中的转基因表现得好像它们在异染色质中一样，而末端反转录转座子阵列中的类似转基因以与插入到常染色质中一致的水平表达。 已知突变会显著增加或减少逆转录转座子添加到染色体末端的频率，这表明该过程受遗传控制。我们已经描述了一个突变，通过增加末端基因转换的频率来增加转座子阵列长度，并且正在使用位置信息来克隆基因。具有长末端反转录转座子阵列的个体具有降低的生育力。 为了试图了解控制端粒稳定性的因素之间的相互作用，我们正在用mutator mu 2进行双突变组合，这增加了一个断裂缺失的频率，这些缺失已经失去了天然端粒并在断裂端形成了新的端粒。第二个突变将是降低端粒稳定性和增加端粒融合的突变。我们将测试新端粒的产生和端粒融合的频率。

Telomeres are nucleoprotein structures at chromosome ends that are required to completely replicate the linear DNA and to distinguish the natural chromosome end from a double strand chromosome break for purposes of DNA repair. In Drosophila, chromosome ends are maintained by the targeted transposition of three retrotransposons, HeT-A, TAHRE, and TART, as well as gene conversion between telomeres. In the wild type, transposition and gene conversion are sufficient to balance the gradual chromosome shortening due to incomplete DNA replication. Mutations are known that drastically increase or decrease the frequency of retrotransposon addition to a chromosome end, suggesting that this process is under genetic control. We have characterized one mutation that increases the frequency of terminal gene conversion, and are using positional information to clone the gene. A transgene inserted into a telomere is subject to repression, termed telomere position effect, TPE. TPE is found in a wide variety of species, including yeast, insects, and humans. In Drosophila, a transgene in the subterminal telomere associated sequence (TAS), or between TAS and the terminal retrotransposon array is repressed and variegates. This variegation appears to be due to an interaction of repression induced by TAS and activation initiated by HeT-A transcription. A telomeric transgene thus provides an assay for this interaction. These transgenes may provide a means to investigate the control of HeT-A transcription and transposition, and thus telomere elongation. Transgenes inserted into TAS behave as if they were in heterochromatin, while similar transgenes in the terminal retrotransposon array express at a level consistent with insertions into euchromatin. Mutations are known that drastically increase or decrease the frequency of retrotransposon addition to a chromosome end, suggesting that this process is under genetic control. We have characterized one mutation that increases the transposon array length by increasiing the frequency of terminal gene conversion, and are using positional information to clone the gene. Individuals with long terminal retrotransposon arrays have decreased fertility. In an attempt to understand the interaction of factors that control telomere stability, we are making double mutation combinations with the mutator, mu2, which increases the frequency of one-break deletions that have lost a natural telomere and formed a new telomere on the broken end. The second mutation will be a mutation that decreases telomere stability and increases telomere fusions. We will test both the generation of new telomeres and the frequency of telomere fusions.