Asano K, Krishnamoorthy T, Phan L, Pavitt G D, Hinnebusch A G
Laboratory of Eukaryotic Gene Regulation, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA.
EMBO J. 1999 Mar 15;18(6):1673-88. doi: 10.1093/emboj/18.6.1673.
In the initiation phase of eukaryotic translation, eIF5 stimulates the hydrolysis of GTP bound to eIF2 in the 40S ribosomal pre-initiation complex, and the resultant GDP on eIF2 is replaced with GTP by the complex nucleotide exchange factor, eIF2B. Bipartite motifs rich in aromatic and acidic residues are conserved at the C-termini of eIF5 and the catalytic (epsilon) subunit of eIF2B. Here we show that these bipartite motifs are important for the binding of these factors, both in vitro and in vivo, to the beta subunit of their common substrate eIF2. We also find that three lysine-rich boxes in the N-terminal segment of eIF2beta mediate the binding of eIF2 to both eIF5 and eIF2B. Thus, eIF5 and eIF2Bepsilon employ the same sequence motif to facilitate interaction with the same segment of their common substrate. In agreement with this, archaea appear to lack eIF5, eIF2B and the lysine-rich binding domain for these factors in their eIF2beta homolog. The eIF5 bipartite motif is also important for its interaction with the eIF3 complex through the NIP1-encoded subunit of eIF3. Thus, the bipartite motif in eIF5 appears to be multifunctional, stimulating its recruitment to the 40S pre-initiation complex through interaction with eIF3 in addition to binding of its substrate eIF2.
在真核生物翻译的起始阶段，eIF5刺激40S核糖体起始前复合物中与eIF2结合的GTP水解，eIF2上产生的GDP被复合核苷酸交换因子eIF2B替换为GTP。富含芳香族和酸性残基的双基序在eIF5的C末端和eIF2B的催化（ε）亚基中保守。在这里，我们表明这些双基序对于这些因子在体外和体内与它们共同底物eIF2的β亚基的结合很重要。我们还发现eIF2β N端片段中的三个富含赖氨酸的框介导eIF2与eIF5和eIF2B的结合。因此，eIF5和eIF2Bε利用相同的序列基序来促进与它们共同底物的同一段的相互作用。与此一致的是，古细菌似乎在其eIF2β同源物中缺乏eIF5、eIF2B以及这些因子的富含赖氨酸的结合域。eIF5双基序对于其通过eIF3的NIP1编码亚基与eIF3复合物的相互作用也很重要。因此，eIF5中的双基序似乎具有多功能，除了结合其底物eIF2外，还通过与eIF3相互作用刺激其募集到40S起始前复合物中。
