Effect of phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 on the function of reversing factor in the initiation of protein synthesis.
Effect of phosphorylation of the alpha-subunit of eukaryotic initiation factor 2 on the function of reversing factor in the initiation of protein synthesis.
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真核起始因子 2 α 亚基磷酸化对蛋白质合成起始中逆转因子功能的影响。
DOI：
10.1073/pnas.80.9.2559
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发表时间：
1983
影响因子：
11.1
通讯作者：
London,IM
中科院分区：
文献类型：
--
作者：
Matts,RL;Levin,DH;London,IM
网织红细胞逆转因子（RF）作为与真核起始因子2（eIF-2）的复合物分离，在恢复血红素缺乏抑制的网织红细胞裂解物中的蛋白质合成中起催化作用。在含有Mg 2+（0.25-0.5 mM）的体外测定混合物中，RF催化二元复合物（eIF-2-GDP）的形成，但当eIF-2被血红素调节激酶磷酸化为eIF-2的α亚基（HRI）时，这种作用受到抑制。更重要的是，RF催化（eIF-2-GDP）的快速解离，这允许GTP交换为GDP，并且在Met-tRNAf的存在下，促进三元复合物（eIF-2-Met-tRNAf X GTP）的形成。然而，通过HRI的二元复合物的磷酸化防止其通过RF解离，因此，三元复合物的形成被抑制。我们的研究结果表明磷酸化的二元复合物[eIF-2（alpha P）.GDP]与RF相互作用形成[RF . eIF-2（α P）]，其不容易解离。RF的这种结合使其不能催化未磷酸化的二元复合物的解离，从而阻断eIF-2的再循环。由于RF以相对于eIF-2的有限浓度存在于裂解物中，因此以这种方式螯合RF可以解释血红素缺陷裂解物中小比例eIF-2的磷酸化足以抑制蛋白质合成的观察结果。
The reticulocyte reversing factor (RF) isolated as a complex with eukaryotic initiation factor 2 (eIF-2) acts catalytically in restoring protein synthesis in reticulocyte lysates inhibited by heme deficiency. In reconstituted in vitro assay mixtures containing Mg2+ (0.25-0.5 mM), RF catalyzes the formation of the binary complex (eIF-2-GDP) but this effect is inhibited when eIF-2 is phosphorylated by the heme-regulated kinase for the alpha-subunit of eIF-2 (HRI). More significantly, RF catalyzes the rapid dissociation of (eIF-2-GDP), which permits the exchange of GTP for GDP and, in the presence of Met-tRNAf, promotes the formation of the ternary complex (eIF-2-Met-tRNAf X GTP). However, phosphorylation of the binary complex by HRI prevents its dissociation by RF and, as a consequence, ternary complex formation is inhibited. Our results indicate that phosphorylated binary complex [eIF-2(alpha P).GDP] interacts with RF to form a [RF . eIF-2(alpha P)] that is not readily dissociable. This binding of RF renders it unavailable to catalyze the dissociation of unphosphorylated binary complex, thereby blocking the recycling of eIF-2. Since RF is present in lysates at a limited concentration relative to that of eIF-2, the sequestering of RF in this manner could account for the observation that the phosphorylation of a small proportion of eIF-2 in heme-deficient lysates is sufficient to inhibit protein synthesis.