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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Adaptation to diverse nitrogen-limited environments by deletion or extrachromosomal element formation of the GAP1 locus
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Adaptation to diverse nitrogen-limited environments by deletion or extrachromosomal element formation of the GAP1 locus

机译：通过缺失或GAP1基因座的染色体外元素形成适应各种氮受限的环境

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摘要

To study adaptive evolution in defined environments, we performed evolution experiments with Saccharomyces cerevisiae (yeast) in nitrogen-limited chemostat cultures. We used DNA microarrays to identify copy-number variation associated with adaptation and observed frequent amplifications and deletions at the GAP1 locus. GAP1 encodes the general amino acid permease, which transports amino acids across the plasma membrane. We identified a self-propagating extrachromosomal circular DNA molecule that results from intrachro-mosomal recombination between long terminal repeats (LTRs) flanking GAP1. Extrachromosomal DNA circles (GAP1~(circle)) contain GAP1. the replication origin ARS1116, and a single hybrid LTR derived from recombination between the two flanking LTRs. Formation of the GAP1~(circle) is associated with deletion of chromosomal GAP1 (gap1 △) and production of a single hybrid LTR at the GAP1 chromosomal lotus. The GAP1~(circle) is selected following prolonged culturing in l-glutamine-limited chemostats in a manner analogous to the selection of oncogenes present on double minutes in human cancers. Clones carrying only the gap1△ allele were selected under various non-amino acid nitrogen limitations including ammonium, urea, and allantoin limitation. Previous studies have shown that the rate of intrachromosomal recombination between tandem repeats is stimulated by transcription of the intervening sequence. The high level of GAP1 expression in nitrogen-limited chemostats suggests that the frequency of GAP1~(circle) and gap1△ generation may be increased under nitrogen-limiting conditions. We propose that this genomic architecture facilitates evolvability of 5. cerevisiae populations exposed to variation in levels and sources of environmental nitrogen.
机译：为了研究在定义的环境中的适应性进化，我们在有限氮的恒化器培养物中用酿酒酵母（酵母）进行了进化实验。我们使用DNA微阵列识别与适应相关的拷贝数变异，并在GAP1基因座处观察到频繁的扩增和缺失。 GAP1编码一般的氨基酸通透酶，该酶在整个质膜上运输氨基酸。我们确定了一种自繁殖的染色体外环状DNA分子，其是由GAP1旁的长末端重复序列（LTR）之间的染色体间重组产生的。染色体外DNA圈（GAP1〜（圈））含有GAP1。复制起点ARS1116，以及从​​两个侧翼LTR之间重组产生的单个杂交LTR。 GAP1〜（圈）的形成与染色体GAP1（gap1△）的缺失和在GAP1染色体莲花上单个杂种LTR的产生有关。在L-谷氨酰胺有限的化学恒温器中长时间培养后，以类似于选择人类癌症中每两分钟存在的致癌基因的方式选择GAP1-。在各种非氨基酸氮限制条件下选择仅携带gap1△等位基因的克隆，包括铵，尿素和尿囊素限制条件。先前的研究表明，插入序列的转录刺激串联重复序列之间的染色体内重组速率。限氮化肥中GAP1的高水平表达表明，在限氮条件下，GAP1〜（○）和gap1△的产生频率可能​​会增加。我们建议，这种基因组结构可促进5.暴露于环境氮水平和来源变化的酿酒酵母种群的进化。

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