Genetic Information Research Institute, Mountain View, CA 94043, USA.
Gene. 2010 Oct 1;465(1-2):9-16. doi: 10.1016/j.gene.2010.06.005. Epub 2010 Jun 21.
LINE-1 (L1) retrotransposons represent the most abundant family of non-LTR retrotransposons in virtually all mammals. The only currently known exception is Platypus, where it is found only in low copy numbers. Autonomous L1s encode two proteins, ORF1p and ORF2p, both of which are required for the transposition of L1s. L1 replicative machinery is also involved in the trans-mobilization of non-autonomous retrotransposons, such as diverse short interspersed repetitive elements (SINEs) and processed pseudogenes. Here, we focus on a unique category of "half -L1" elements (HAL1s), which encode ORF1p but not ORF2p. HAL1s are present both in placental mammals and marsupials. We demonstrate that HAL1s originated independently several times during the evolution of mammals. The youngest mammalian HAL1 elements analyzed in this paper were identified in the guinea pig genome. Our analysis strongly suggests that HAL1-encoded ORF1p is essential for the transposition of HAL1s and indicates that the evolution of ORF1p in HAL1s is faster than in L1s. The implications of HAL1 for the evolution of L1 elements and the host genomes are discussed.
LINE-1（L1）逆转录转座子是几乎所有哺乳动物中最丰富的非 LTR 逆转录转座子家族。目前唯一已知的例外是鸭嘴兽，其仅以低拷贝数存在。自主 L1 编码两种蛋白质，ORF1p 和 ORF2p，两者均为 L1 转座所必需。L1 复制机制还参与非自主逆转录转座子的转移动，如各种短散布重复元件（SINEs）和加工假基因。在这里，我们重点关注一类独特的“半 L1”元件（HAL1s），其编码 ORF1p 但不编码 ORF2p。HAL1s 存在于胎盘哺乳动物和有袋动物中。我们证明 HAL1s 在哺乳动物的进化过程中独立地多次起源。本文分析的最年轻的哺乳动物 HAL1 元件在豚鼠基因组中被鉴定出来。我们的分析强烈表明，HAL1 编码的 ORF1p 对 HAL1 的转座是必不可少的，并表明 HAL1 中 ORF1p 的进化速度比 L1 中的进化速度快。讨论了 HAL1 对 L1 元件和宿主基因组进化的影响。
