Structural biology department, National Research Center 'Kurchatov Institute', Moscow 123182, Russia.
Institute of Protein Research RAS, Pushchino, Moscow Region 142290, Russia.
Nucleic Acids Res. 2023 Jan 25;51(2):908-918. doi: 10.1093/nar/gkac1208.
Polyribosomes, the groups of ribosomes simultaneously translating a single mRNA molecule, are very common in both, prokaryotic and eukaryotic cells. Even in early EM studies, polyribosomes have been shown to possess various spatial conformations, including a ring-shaped configuration which was considered to be functionally important. However, a recent in situ cryo-ET analysis of predominant regular inter-ribosome contacts did not confirm the abundance of ring-shaped polyribosomes in a cell cytoplasm. To address this discrepancy, here we analyzed the cryo-ET structure of polyribosomes in diluted lysates of HeLa cells. It was shown that the vast majority of the ribosomes were combined into polysomes and were proven to be translationally active. Tomogram analysis revealed that circular polyribosomes are indeed very common in the cytoplasm, but they mostly possess pseudo-regular structures without specific inter-ribosomal contacts. Although the size of polyribosomes varied widely, most circular polysomes were relatively small in size (4-8 ribosomes). Our results confirm the recent data that it is cellular mRNAs with short ORF that most commonly form circular structures providing an enhancement of translation.
多聚核糖体，即同时翻译单个 mRNA 分子的核糖体群，在原核细胞和真核细胞中都非常常见。即使在早期的电子显微镜研究中，也已经表明多聚核糖体具有各种空间构象，包括环形构象，这种构象被认为具有重要的功能。然而，最近对核糖体间常见的规则接触的原位冷冻电镜分析并没有证实细胞质中环形多聚核糖体的丰富程度。为了解决这一差异，我们在这里分析了稀释的 HeLa 细胞裂解物中多聚核糖体的冷冻电镜结构。结果表明，绝大多数核糖体被组合成多核糖体，并被证明具有翻译活性。断层扫描分析表明，环形多聚核糖体在细胞质中确实非常普遍，但它们大多具有没有特定核糖体间接触的假规则结构。尽管多聚核糖体的大小差异很大，但大多数环形多核糖体的大小相对较小（4-8 个核糖体）。我们的结果证实了最近的数据，即具有短 ORF 的细胞 mRNA 最常形成环形结构，从而增强翻译。
