Release of nonstop ribosomes is essential.
Release of nonstop ribosomes is essential.
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DOI：
10.1128/mbio.01916-14
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发表时间：
2014-11-11
期刊：
影响因子：
6.4
通讯作者：
Keiler KC
中科院分区：
文献类型：
--
作者：
Feaga HA;Viollier PH;Keiler KC
细菌核糖体经常翻译到mRNA的3′端，而不终止于终止密码子。几乎所有的细菌都使用基于transfer-messenger RNA（tmRNA）的转译途径来释放这些“不间断”的核糖体并维持蛋白质合成能力。反式翻译在某些物种中是必需的，但在其它物种中，如新月柄杆菌，反式翻译可以失活。为了确定为什么反式翻译在新月形隐球菌中被抑制，使用Tn-seq筛选来鉴定在缺乏ssrA（编码tmRNA的基因）的细胞中特异性改变生长的基因。其中一个基因CC 1214在ΔssrA细胞中是必需的。纯化后的CC 1214蛋白在体外可持续释放核糖体。CC 1214是大肠杆菌ArfB蛋白的同源物，并且使用CC 1214序列，在大多数细菌门中鉴定了ArfB同源物。大多数物种中ssrA已经删除含有ArfB同源物，这表明在大多数或所有细菌中，不间断的核糖体释放可能是必不可少的。在大的系统发育距离上保守的基因预期赋予选择优势。反式翻译所需的基因，ssrA和smpB，已经在>99%的测序细菌基因组中发现，这表明它们具有广泛的重要性。然而，这些基因可以在某些物种中删除而不丧失生存能力。对新月形隐球菌ArfB的鉴定和表征揭示了为什么反式翻译在新月形隐球菌中不是必需的，并表明当反式翻译受损时，许多其他细菌可能使用ArfB生存。
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. 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.