Telomeric Position Effects in Drosophila

真核生物的染色体有不同的紧密连接区域，称为异染色质和常染色质。异染色质具有重复DNA密度高、基因少、转录少的特点。活性基因，其中大部分在常染色质中发现，如果它们被移到异染色质区域，就会失活。这种效应被称为位置效应差异(PEV)，已经在果蝇-黑腹果蝇身上得到了广泛的研究。有证据表明，真核细胞染色体末端的端粒区域是特化的异染色样结构域。该项目在果蝇中使用端粒PEV，通过鉴定端粒非组蛋白和与这些蛋白质结合的端粒DNA序列来研究端粒染色质。在端粒序列两侧的白色眼色基因将在非端粒位置整合，并将比较有无端粒序列的该基因的表达。第二种方法是定位必要的和/或足够结合HP1的DNA序列，HP1是一种在其他实验室中具有特征的蛋白质，它与染色质缩合有关。这个项目的主要目标是识别端粒蛋白及其结合的DNA序列，但由此产生的数据也将与更广泛的问题相关，即基因表达如何通过染色体凝聚来调节。这种机制被认为对真核生物的正常发育至关重要。

Chromosomes of eukaryotes have regions of differing compaction termed heterochromatin and euchromatin. Heterochromatin has a high density of repetitious DNA, few genes and little transcription. Active genes, most of which are found in the euchromatin, are inactivated if they are removed to heterochromatic regions. This effect, called position effect variegation (PEV), has been extensively studied in Drosophila melanogaster, the fruit fly. There is evidence that the telomeric regions at the ends of eukaryotic chromosomes are specialized heterochromatic-like domains. The project proposed uses telomeric PEV in Drosophila to investigate telomeric chromatin by identification of telomeric non- histone proteins and telomeric DNA sequences which bind those proteins. A white eye color gene flanked by telomeric sequences will be integrated at non-telomeric locations and the expression of that gene with and without the telomeric sequences will be compared. A second approach will be to localize the DNA sequences necessary and/or sufficient to bind HP1, a protein characterized in other laboratories, which is implicated in chromatin condensation. %%% The primary objective of this project is to identify telomeric proteins and the DNA sequences to which they bind, but the resulting data will also be relevant to the broader question of how gene expression is regulated by chromosome condensation. Such a mechanism is thought to be critical to normal development of eukaryotic organisms.