Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA.
Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA.
Cell Rep. 2019 Jul 2;28(1):39-50.e4. doi: 10.1016/j.celrep.2019.05.111.
Hcr1/eIF3j is a sub-stoichiometric subunit of eukaryotic initiation factor 3 (eIF3) that can dissociate the post-termination 40S ribosomal subunit from mRNA in vitro. We examine this ribosome recycling role in vivo by ribosome profiling and reporter assays and find that loss of Hcr1 leads to reinitiation of translation in 3' UTRs, consistent with a defect in recycling. However, the defect appears to be in the recycling of the 60S subunit, rather than the 40S subunit, because reinitiation does not require an AUG codon and is suppressed by overexpression of the 60S dissociation factor Rli1/ABCE1. Consistent with a 60S recycling role, overexpression of Hcr1 cannot compensate for loss of 40S recycling factors Tma64/eIF2D and Tma20/MCT-1. Intriguingly, loss of Hcr1 triggers greater expression of RLI1 via an apparent feedback loop. These findings suggest Hcr1/eIF3j is recruited to ribosomes at stop codons and may coordinate the transition to a new round of translation.
Hcr1/eIF3j 是真核起始因子 3（eIF3）的亚基，其在体外可以使终止后的 40S 核糖体亚基从 mRNA 上解离。我们通过核糖体图谱和报告基因检测来研究体内的这种核糖体回收作用，发现 Hcr1 的缺失会导致 3'UTR 中的翻译重新起始，这与回收缺陷一致。然而，这种缺陷似乎发生在 60S 亚基的回收中，而不是 40S 亚基的回收中，因为重新起始不需要 AUG 密码子，并且受到 60S 解离因子 Rli1/ABCE1 过表达的抑制。与 60S 回收作用一致，Hcr1 的过表达不能补偿 40S 回收因子 Tma64/eIF2D 和 Tma20/MCT-1 的缺失。有趣的是，Hcr1 的缺失通过一个明显的反馈回路触发了 RLI1 的更高表达。这些发现表明，Hcr1/eIF3j 在终止密码子处被招募到核糖体上，可能协调向新轮翻译的过渡。
