Pavel Jedlička, Viktor Tokan, Iva Kejnovská, Roman Hobza, Eduard Kejnovský
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引用次数: 2
Abstract
Background: Canonical telomeres (telomerase-synthetised) are readily forming G-quadruplexes (G4) on the G-rich strand. However, there are examples of non-canonical telomeres among eukaryotes where telomeric tandem repeats are invaded by specific retrotransposons. Drosophila melanogaster represents an extreme example with telomeres composed solely by three retrotransposons-Het-A, TAHRE and TART (HTT). Even though non-canonical telomeres often show strand biased G-distribution, the evidence for the G4-forming potential is limited.
Results: Using circular dichroism spectroscopy and UV absorption melting assay we have verified in vitro G4-formation in the HTT elements of D. melanogaster. Namely 3 in Het-A, 8 in TART and 2 in TAHRE. All the G4s are asymmetrically distributed as in canonical telomeres. Bioinformatic analysis showed that asymmetric distribution of potential quadruplex sequences (PQS) is common in telomeric retrotransposons in other Drosophila species. Most of the PQS are located in the gag gene where PQS density correlates with higher DNA sequence conservation and codon selection favoring G4-forming potential. The importance of G4s in non-canonical telomeres is further supported by analysis of telomere-associated retrotransposons from various eukaryotic species including green algae, Diplomonadida, fungi, insects and vertebrates. Virtually all analyzed telomere-associated retrotransposons contained PQS, frequently with asymmetric strand distribution. Comparison with non-telomeric elements showed independent selection of PQS-rich elements from four distinct LINE clades.
Conclusion: Our findings of strand-biased G4-forming motifs in telomere-associated retrotransposons from various eukaryotic species support the G4-formation as one of the prerequisites for the recruitment of specific retrotransposons to chromosome ends and call for further experimental studies.
背景:规范端粒(端粒酶合成)很容易在富含g的链上形成g -四联体(G4)。然而,在真核生物中有非规范端粒的例子,其中端粒串联重复序列被特定的反转录转座子入侵。黑腹果蝇代表了一个极端的例子,其端粒仅由三个反转录转座子- het - a, TAHRE和TART (HTT)组成。尽管非规范端粒经常表现出链偏g分布,但关于g4形成潜力的证据有限。结果:采用圆二色光谱法和紫外吸收熔融法,证实了黑胃草中HTT元素的g4生成。即Het-A有3个,TART有8个,tare有2个。所有的G4s都不对称地分布在规范端粒中。生物信息学分析表明,潜在四重体序列(PQS)的不对称分布在其他果蝇物种的端粒反转录转座子中也很常见。大多数PQS位于gag基因,PQS密度与较高的DNA序列保守性和有利于g4形成潜力的密码子选择相关。G4s在非规范端粒中的重要性进一步得到了来自各种真核生物物种(包括绿藻、外交家、真菌、昆虫和脊椎动物)的端粒相关反转录转座子的分析的支持。几乎所有分析的端粒相关的反转录转座子都含有PQS,通常具有不对称链分布。与非端粒元素的比较表明,4个不同的LINE分支中pqs丰富的元素是独立选择的。结论:我们在不同真核物种的端粒相关的反转录转座子中发现了链偏置的g4形成基序,支持g4的形成是特定的反转录转座子募集到染色体末端的先决条件之一,需要进一步的实验研究。
期刊介绍:
Mobile DNA is an online, peer-reviewed, open access journal that publishes articles providing novel insights into DNA rearrangements in all organisms, ranging from transposition and other types of recombination mechanisms to patterns and processes of mobile element and host genome evolution. In addition, the journal will consider articles on the utility of mobile genetic elements in biotechnological methods and protocols.