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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Evolution of diverse mechanisms for protecting chromosome ends by Drosophila TART telomere retrotransposons
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Evolution of diverse mechanisms for protecting chromosome ends by Drosophila TART telomere retrotransposons

机译：果蝇TART端粒逆转座子保护染色体末端的各种机制的演变

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摘要

The retrotransposons HeT-A, TART, and TAHRE, which maintain Drosophila telomeres, transpose specifically onto chromosome ends to form long arrays that extend the chromosome and compensate for terminal loss. Because they transpose by target-primed reverse transcription, each element is oriented so that its 5' end serves as the extreme end of the chromosome until another element transposes to occupy the terminal position. Thus 5' sequences are at risk for terminal erosion while the element is at the chromosome end. Here we report that TART elements in Drosophila melanogaster and Drosophila virilis show species-specific innovations in promoter architecture that buffer loss of sequence exposed at chromosome ends. The two elements have evolved different ways to effect this protection. The D. virilis TART (TART~(vir)) promoter is found in the 3' UTR of the element directly upstream of the element transcribed. Transcription starts within the upstream element so that a Tag" of extra sequence is added to the 5' end of the newly transcribed RNA. This Tag provides expendable sequence to buffer end erosion of essential 5' sequence after the RNA is reverse transcribed onto the chromosome. In contrast, the D. melanogaster TART (TART~(mel)) promoter initiates transcription deep within the 5' UTR, but the element is able to replace and extend the 5' UTR sequence by copying sequence from its 3' UTR, we believe while being reverse transcribed onto the chromosome end. Astonishingly, end-protection in TART~(vir) and HeT-A~(mel) are essentially identical (using Tags), whereas HeT-A"'r is clearly protected from end erosion by an as-yet-unspecified program.
机译：维持果蝇端粒的逆转座子HeT-A，TART和TAHRE特异地转座到染色体末端上，形成长的阵列，延伸了染色体并补偿了末端损失。因为它们通过靶标引发的逆转录进行转座，所以每个元件都经过定向，以使其5'端成为染色体的末端，直到另一个元件转座以占据末端位置。因此，当元件位于染色体末端时，5'序列有遭受末端侵蚀的风险。在这里，我们报告果蝇和果蝇的TART元素显示启动子体系结构中的物种特定的创新，以缓冲暴露在染色体末端的序列丢失。这两个要素发展了不同的方式来实现这种保护。 D. virilis TART（TART_（vir））启动子位于转录元件正上游的元件3'UTR中。转录在上游元件中开始，因此在新转录的RNA的5'末端添加了额外序列的标签“。此标签提供了可消耗的序列，以缓冲RNA被逆转录到染色体上后必不可少的5'序列的末端侵蚀。相比之下，D。melanogaster TART（TART〜（mel））启动子可在5'UTR内深处启动转录，但该元件能够通过复制其3'UTR中的序列来替换和扩展5'UTR序列，令人惊讶的是，令人惊讶的是，TART_（vir）和HeT-A〜（mel）的末端保护本质上是相同的（使用标签），而HeT-A“'r显然受到了末端侵蚀的保护通过尚未指定的程序。

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