The Nsp1 protein of SARS-CoV-2 regulates the translation of host and viral mRNAs in cells. Nsp1 inhibits host translation initiation by occluding the entry channel of the 40S ribosome subunit. The structural study of SARS-CoV-2 Nsp1-ribosomal complexes reported post-termination 80S complex containing Nsp1 and the eRF1 and ABCE1 proteins. Considering the presence of Nsp1 in the post-termination 80S ribosomal complex simultaneously with eRF1, we hypothesized that Nsp1 may be involved in translation termination. Using a cell-free translation system and reconstituted in vitro translation system, we show that Nsp1 stimulates translation termination in the stop codon recognition stage at all three stop codons. This stimulation targets the release factor 1 (eRF1) and does not affect the release factor 3 (eRF3). The activity of Nsp1 in translation termination is provided by its N-terminal domain and the minimal required part of eRF1 is NM domain. We assume that biological meaning of Nsp1 activity in translation termination is binding with the 80S ribosomes translating host mRNAs and removal them from the pool of the active ribosomes.

中文翻译：

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Nsp1的SARS-CoV-2刺激宿主翻译终止。

SARS-CoV-2的Nsp1蛋白调节细胞中宿主和病毒mRNA的翻译。Nsp1通过阻塞40S核糖体亚基的进入通道来抑制宿主翻译起始。SARS-CoV-2 Nsp1-核糖体复合物的结构研究报告了终止后的80S复合物，其中包含Nsp1以及eRF1和ABCE1蛋白。考虑到Nsp1在终止后80S核糖体复合物中与eRF1同时存在，我们假设Nsp1可能参与翻译终止。使用无细胞翻译系统和重构的体外翻译系统，我们显示Nsp1在所有三个终止密码子的终止密码子识别阶段均刺激翻译终止。这种刺激的目标是释放因子1（eRF1），而不会影响释放因子3（eRF3）。Nsp1在翻译终止中的活性由其N末端域提供，而eRF1所需的最少部分是NM域。我们假设翻译终止中Nsp1活性的生物学意义与翻译宿主mRNA的80S核糖体结合并将其从活性核糖体库中除去。