Telomeric Position Effects in Drosophila

真核生物的染色体有不同的压实区域，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，大多数在常染色质中发现，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变异（PEV），已经在果蝇中得到了广泛的研究。有证据表明，真核生物染色体末端的端粒区域是特化的异色样结构域。本项目拟利用果蝇的端粒PEV，通过鉴定端粒非组蛋白和结合这些蛋白的端粒DNA序列来研究端粒染色质。一个带有端粒序列的白眼色基因将被整合到非端粒位置，并比较该基因在有端粒序列和没有端粒序列时的表达。第二种方法是定位与HP1结合所必需和/或足够的DNA序列，HP1是其他实验室鉴定的一种蛋白质，与染色质凝聚有关。该项目的主要目标是鉴定端粒蛋白及其结合的DNA序列，但所得数据也将与染色体凝聚如何调节基因表达这一更广泛的问题相关。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.