Ptushkina Marina, Malys Naglis, McCarthy John E G
Posttranscriptional Control Group, Department of Biomolecular Sciences, UMIST, Manchester, UK.
EMBO Rep. 2004 Mar;5(3):311-6. doi: 10.1038/sj.embor.7400088. Epub 2004 Feb 6.
Cap-binding proteins of the elF4E family are generally involved in mediating ribosome recruitment to capped mRNA via an interaction with the initiation factor elF4G. However, Schizosaccharomyces pombe has two elF4E isoforms, one of which (elF4E2, encoded by tif452) has a relatively low affinity for elF4G. We show that tif452 is required for specific stress responses. An S. pombe, tif452delta mutant manifests slow growth under conditions of nutrient, temperature and salt stress. elF4E2 shows a distinct subcellular distribution to elF4E1, the cap-binding factor that is required for mainstream translation. In response to salt stress, the cellular level of elF4E2 increases, whereas the amount of intact elF4G decreases, leaving elF4E2 as the predominant elF4E isoform in a cell deficient in ElF4G. The presence of elF4E2 modifies the competence of S. pombe ribosomes to translate mRNAs with structured leaders in vivo. The tif452 promoter has putative stress-response (T-rich) motifs, whereas elF4E2 seems to be a new type of stress-response factor.
真核起始因子4E（eIF4E）家族的帽结合蛋白通常通过与起始因子eIF4G相互作用，介导核糖体与加帽mRNA的结合。然而，裂殖酵母有两种eIF4E亚型，其中一种（由tif452编码的eIF4E2）对eIF4G的亲和力相对较低。我们发现tif452是特定应激反应所必需的。裂殖酵母tif452缺失突变体在营养、温度和盐胁迫条件下生长缓慢。eIF4E2与主流翻译所需的帽结合因子eIF4E1表现出不同的亚细胞分布。在盐胁迫下，eIF4E2的细胞水平增加，而完整eIF4G的量减少，使得eIF4E2成为eIF4G缺陷细胞中主要的eIF4E亚型。eIF4E2的存在改变了裂殖酵母核糖体在体内翻译具有结构化前导序列mRNA的能力。tif452启动子具有假定的应激反应（富含T）基序，而eIF4E2似乎是一种新型的应激反应因子。
