Ghosh Arnab, Jindal Supriya, Bentley Amber A, Hinnebusch Alan G, Komar Anton A
Center for Gene Regulation in Health and Disease, Department of Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, OH 44115, USA.
Laboratory of Gene Regulation and Development, Eunice K. Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Nucleic Acids Res. 2014 Jul;42(13):8537-55. doi: 10.1093/nar/gku550. Epub 2014 Jun 19.
Conserved ribosomal proteins frequently harbor additional segments in eukaryotes not found in bacteria, which could facilitate eukaryotic-specific reactions in the initiation phase of protein synthesis. Here we provide evidence showing that truncation of the N-terminal domain (NTD) of yeast Rps5 (absent in bacterial ortholog S7) impairs translation initiation, cell growth and induction of GCN4 mRNA translation in a manner suggesting incomplete assembly of 48S preinitiation complexes (PICs) at upstream AUG codons in GCN4 mRNA. Rps5 mutations evoke accumulation of factors on native 40S subunits normally released on conversion of 48S PICs to 80S initiation complexes (ICs) and this abnormality and related phenotypes are mitigated by the SUI5 variant of eIF5. Remarkably, similar effects are observed by substitution of Lys45 in the Rps5-NTD, involved in contact with Rps16, and by eliminating the last two residues of the C-terminal tail (CTT) of Rps16, believed to contact initiator tRNA base-paired to AUG in the P site. We propose that Rps5-NTD-Rps16-NTD interaction modulates Rps16-CTT association with Met-tRNAi (Met) to promote a functional 48S PIC.
在真核生物中，保守的核糖体蛋白常常带有细菌中未发现的额外片段，这可能有助于在蛋白质合成起始阶段发生真核生物特有的反应。在此，我们提供的证据表明，酵母Rps5的N端结构域（NTD）（细菌直系同源物S7中不存在）的截短会损害翻译起始、细胞生长以及GCN4 mRNA翻译的诱导，其方式表明在GCN4 mRNA的上游AUG密码子处48S预起始复合物（PIC）组装不完全。Rps5突变会导致通常在48S PIC转化为80S起始复合物（IC）时释放的因子在天然40S亚基上积累，而eIF5的SUI5变体可减轻这种异常及相关表型。值得注意的是，通过替换Rps5-NTD中与Rps16接触的Lys45，以及去除Rps16 C端尾巴（CTT）的最后两个残基（据信该残基与P位点中与AUG碱基配对的起始tRNA接触），也观察到了类似的效果。我们提出，Rps5-NTD-Rps16-NTD相互作用调节Rps16-CTT与Met-tRNAi（Met）的结合，以促进功能性48S PIC的形成。
