Short interspersed elements (SINEs) are ubiquitous components of eukaryotic genomes. SINEs are composite transposable elements that are mobilized by non-long terminal repeat (non-LTR) retrotransposons, also called long interspersed elements (LINEs). The 3′ part of SINEs usually originated from that of counterpart non-LTR retrotransposons. The 5′ part of SINEs mostly originated from small RNA genes. SINE1 is a group of SINEs whose 5′ part originated from 7SL RNA, and is represented by primate Alu and murine B1. Well-defined SINE1 has been found only from Euarchontoglires, a group of mammals, in contrast to the wide distribution of SINE2, which has a tRNA-derived sequence, from animals to plants to protists. Both Alu and B1 are mobilized by L1-type non-LTR retrotransposons, which are the only lineage of autonomous non-LTR retrotransposons active in these mammalian lineages. Here a new lineage of SINE1 is characterized from the seashore hagfish Eptatretus burgeri genome. This SINE1 family, designated SINE1-1_EBu, is young, and is transposed by RTE-type non-LTR retrotransposon, not L1-type. Comparison with other SINE families from hagfish indicated the birth of SINE1-1_EBu through chimera formation of a 7SL RNA-derived sequence and an older tRNA-derived SINE family. It reveals parallel evolution of SINE1 in two vertebrate lineages with different autonomous non-LTR retrotransposon partners. The comparison between two SINE1 lineages supports that the RNA secondary structure of the Alu domain of 7SL RNA is required for the efficient retrotransposition. The hagfish SINE1 is the first evident SINE1 family found outside of Euarchontoglires. Independent evolution of SINE1 with similar RNA secondary structure originated in 7SL RNA indicates the functional importance of 7SL RNA-derived sequence in the proliferation of SINEs.

中文翻译：

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盲鳗基因组揭示了 7SL RNA 衍生的 SINE 的平行进化。

短散在元素 (SINE) 是真核生物基因组中普遍存在的成分。SINE 是复合转座因子，由非长末端重复 (non-LTR) 反转录转座子移动，也称为长散在元件 (LINE)。SINE 的 3' 部分通常来源于对应的非 LTR 反转录转座子。SINEs的5'部分主要来源于小RNA基因。SINE1是一组SINE，其5'部分来源于7SL RNA，以灵长类Alu和鼠类B1为代表。定义明确的 SINE1 仅在 Euarchontoglires（一组哺乳动物）中发现，与 SINE2 的广泛分布形成对比，SINE2 具有从动物到植物再到原生生物的 tRNA 衍生序列。Alu 和 B1 都被 L1 型非 LTR 反转录转座子调动，这是在这些哺乳动物谱系中活跃的自主非 LTR 反转录转座子的唯一谱系。在这里，一个新的 SINE1 谱系的特征来自海滨盲鳗 Eptatretus burgeri 基因组。这个 SINE1 家族，命名为 SINE1-1_EBu，是年轻的，由 RTE 型非 LTR 反转录转座子转座，而不是 L1 型。与来自盲鳗的其他 SINE 家族的比较表明，SINE1-1_EBu 通过 7SL RNA 衍生序列和较老的 tRNA 衍生 SINE 家族的嵌合形成而诞生。它揭示了 SINE1 在两个具有不同自主非 LTR 反转录转座子伙伴的脊椎动物谱系中的平行进化。两个 SINE1 谱系之间的比较支持 7SL RNA 的 Alu 结构域的 RNA 二级结构是有效反转录转座所必需的。盲鳗 SINE1 是在 Euarchontoglires 之外发现的第一个明显的 SINE1 家族。源自 7SL RNA 的具有相似 RNA 二级结构的 SINE1 的独立进化表明 7SL RNA 衍生序列在 SINE 增殖中的功能重要性。