Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, Rhode Island.
Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island.
Biophys J. 2021 Jun 1;120(11):2181-2191. doi: 10.1016/j.bpj.2021.03.028. Epub 2021 Mar 31.
Long interspersed nuclear element-1 (L1) is a retrotransposable element that autonomously replicates in the human genome, resulting in DNA damage and genomic instability. Activation of L1 in senescent cells triggers a type I interferon response and age-associated inflammation. Two open reading frames encode an ORF1 protein functioning as messenger RNA chaperone and an ORF2 protein providing catalytic activities necessary for retrotransposition. No function has been identified for the conserved, disordered N-terminal region of ORF1. Using microscopy and NMR spectroscopy, we demonstrate that ORF1 forms liquid droplets in vitro in a salt-dependent manner and that interactions between its N-terminal region and coiled-coil domain are necessary for phase separation. Mutations disrupting blocks of charged residues within the N-terminus impair phase separation, whereas some mutations within the coiled-coil domain enhance phase separation. Demixing of the L1 particle from the cytosol may provide a mechanism to protect the L1 transcript from degradation.
长散在核元件-1（L1）是一种逆转录转座子，能够在人类基因组中自主复制，导致 DNA 损伤和基因组不稳定性。衰老细胞中 L1 的激活会引发 I 型干扰素反应和与年龄相关的炎症。两个开放阅读框编码一种 ORF1 蛋白，作为信使 RNA 伴侣发挥作用，另一种 ORF2 蛋白提供逆转录转座所必需的催化活性。ORF1 的保守、无序的 N 端区域的功能尚未确定。通过显微镜和 NMR 光谱学，我们证明 ORF1 在体外以盐依赖性的方式形成液滴，并且其 N 端区域与卷曲螺旋结构域之间的相互作用对于相分离是必要的。破坏 N 端带电荷残基块的突变会损害相分离，而卷曲螺旋结构域内的一些突变会增强相分离。L1 颗粒从细胞质中的去混合可能为保护 L1 转录本免受降解提供了一种机制。
