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Release of Nonstop Ribosomes Is Essential

机译：不断释放核糖体至关重要

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Bacterial ribosomes frequently translate to the 3′ end of an mRNA without terminating at a stop codon. Almost all bacteria use the transfer-messenger RNA (tmRNA)-based trans-translation pathway to release these “nonstop” ribosomes and maintain protein synthesis capacity. trans-translation is essential in some species, but in others, such as Caulobacter crescentus, trans-translation can be inactivated. To determine why trans-translation is dispensable in C.?crescentus, a Tn-seq screen was used to identify genes that specifically alter growth in cells lacking ssrA, the gene encoding tmRNA. One of these genes, CC1214, was essential in ΔssrA cells. Purified CC1214 protein could release nonstop ribosomes in vitro. CC1214 is a homolog of the Escherichia coli ArfB protein, and using the CC1214 sequence, ArfB homologs were identified in the majority of bacterial phyla. Most species in which ssrA has been deleted contain an ArfB homolog, suggesting that release of nonstop ribosomes may be essential in most or all bacteria. >IMPORTANCE Genes that are conserved across large phylogenetic distances are expected to confer a selective advantage. The genes required for trans-translation, ssrA and smpB, have been found in >99% of sequenced bacterial genomes, suggesting that they are broadly important. However, these genes can be deleted in some species without loss of viability. The identification and characterization of C.?crescentus ArfB reveals why trans-translation is not essential in C.?crescentus and suggests that many other bacteria are likely to use ArfB to survive when trans-translation is compromised.
机译：细菌核糖体通常翻译成mRNA的3'末端而不终止于终止密码子。几乎所有细菌都使用基于传递信使RNA（tmRNA）的 trans -翻译途径释放这些“不间断”的核糖体并维持蛋白质合成能力。在某些物种中， trans -翻译是必不可少的，但在其他物种中，例如 Caulobacter crescentus ， trans -翻译可以失活。为了确定为什么在 C.crescentus 中不需要 trans -翻译，使用Tn-seq筛选来鉴定特异性改变缺乏 ssrA < / em>，即编码tmRNA的基因。其中一个基因 CC1214 对Δ ssrA 细胞至关重要。纯化的CC1214蛋白可在体外 释放不间断的核糖体。 CC1214是大肠杆菌 ArfB蛋白的同源物，使用CC1214序列，可以在大多数细菌门中鉴定出ArfB同源物。删除了 ssrA 的大多数物种都含有ArfB同源物，这表明不间断核糖体的释放可能对大多数或所有细菌都是必不可少的。 >重要：在较大的系统发生距离上保守的基因有望带来选择优势。在超过99％的测序细菌基因组中发现了 trans -翻译， ssrA 和 smpB 所需的基因，这表明它们具有广泛的意义重要。但是，可以在某些物种中删除这些基因而不会丧失生存力。对 C.crescentus ArfB的鉴定和表征揭示了为什么 trans -翻译在 C.crescentus 中不是必需的，并暗示了许多其他细菌 trans -翻译受到威胁时，很可能会使用ArfB生存。

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