Transcription of endogenous and exogenous R2 elements in the rRNA gene locus of Drosophila melanogaster
Transcription of endogenous and exogenous R2 elements in the rRNA gene locus of Drosophila melanogaster
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DOI：
10.1128/mcb.23.11.3825-3836.2003
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发表时间：
2003-06-01
影响因子：
5.3
通讯作者：
Eickbush, TH
中科院分区：
文献类型：
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作者：
Eickbush, DG;Eickbush, TH
R2反转录转座子插入到形成昆虫核仁的rRNA编码单位（rDNA单位）中。我们利用果蝇的R2整合系统来研究整合到28S rRNA基因R2靶位点的外源序列的转录。外源序列共转录。显著不同的水平，其紧密地与内源性RI和R2元件的转录水平相关。转录水平与未插入的rDNA单位的数量呈负相关，这个数字的变化已经带来了由R2整合系统本身。每X染色体少至20个未插入的rDNA单位的女性的内源性和外源性插入序列的表达水平比每染色体包含超过80个未插入的rDNA单位的线高2个数量级。R2插入只有167 bp的长度表现出这一范围的转录调控。对男性转录水平的分析表明，Y染色体上的R2插入并没有下调到与X染色体上的插入相同的程度。这些结果表明，rDNA单位的转录可以受到严格的调控，但随着细胞接近生存所需的未插入基因的最小数量，这种调控逐渐被打破。
R2 retrotransposons insert into the rRNA-encoding units (rDNA units) that form the nucleoli of insects. We have utilized an R2 integration system in Drosophila melanogaster to study transcription of foreign sequences integrated into the R2 target site of the 28S rRNA genes. The exogenous sequences were cotranscribed at. dramatically different levels which closely paralleled the level of transcription of the endogenous RI and R2 elements. Transcription levels were inversely correlated with the number of uninserted rDNA units, variation in this number having been brought about by the R2 integration system itself. Females with as few as 20 uninserted rDNA units per X chromosome had expression levels of endogenous and exogenous insertion sequences that were 2 orders of magnitude higher than lines that contained over 80 uninserted rDNA units per chromosome. R2 insertions only 167 bp in length exhibited this range of transcriptional regulation. Analysis of transcript levels in males suggested R2 insertions on the Y chromosome are not down-regulated to the same extent as insertions on the X chromosome. These results suggest that transcription of the rDNA units can be tightly regulated, but this regulation gradually breaks down as the cell approaches the minimum number of uninserted genes needed for survival.