Role of the N- and C-terminal extensions on the activity of mammalian mitochondrial translational initiation factor 3.
Role of the N- and C-terminal extensions on the activity of mammalian mitochondrial translational initiation factor 3.
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DOI：
10.1093/nar/gki1007
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发表时间：
2005
影响因子：
14.9
通讯作者：
Spremulli LL
中科院分区：
文献类型：
--
作者：
Bhargava K;Spremulli LL
哺乳动物线粒体翻译起始因子3（IF 3 mt）在IF 2 mt、fMet-tRNA和poly（A，U，G）存在下促进线粒体55 S核糖体上起始复合物的形成。IF 3 mt的成熟形式预测为247个残基。IF 3 mt与细菌IF 3的比对表明其具有与细菌因子具有20-30%同一性的中心区域。与细菌IF 3相比，IF 3 mt的N-和C-末端均具有约30个残基的延伸。为了检查延伸在IF 3 mt上的作用，制备缺失构建体，其中N-末端延伸、C-末端延伸或两个延伸都被缺失。这些截短的衍生物在促进起始复合物形成方面比IF 3 mt的成熟形式稍微更活跃。线粒体28 S亚基具有在mRNA不存在的情况下结合fMet-tRNA的能力。IF 3 mt促进在mRNA不存在下结合的fMet-tRNA的解离。IF 3 mt的这种活性需要该因子的C-末端延伸。线粒体28 S亚基也独立于fMet-tRNA或添加的起始因子结合mRNA。IF 3 mt对这些复合物的形成没有影响，并且一旦形成就不能解离它们。这些观察结果导致了一个新的模型IF 3 mt在线粒体翻译起始的功能。
Mammalian mitochondrial translational initiation factor 3 (IF3mt) promotes initiation complex formation on mitochondrial 55S ribosomes in the presence of IF2mt, fMet-tRNA and poly(A,U,G). The mature form of IF3mt is predicted to be 247 residues. Alignment of IF3mt with bacterial IF3 indicates that it has a central region with 20–30% identity to the bacterial factors. Both the N- and C-termini of IF3mt have extensions of ∼30 residues compared with bacterial IF3. To examine the role of the extensions on IF3mt, deletion constructs were prepared in which the N-terminal extension, the C-terminal extension or both extensions were deleted. These truncated derivatives were slightly more active in promoting initiation complex formation than the mature form of IF3mt. Mitochondrial 28S subunits have the ability to bind fMet-tRNA in the absence of mRNA. IF3mt promotes the dissociation of the fMet-tRNA bound in the absence of mRNA. This activity of IF3mt requires the C-terminal extension of this factor. Mitochondrial 28S subunits also bind mRNA independently of fMet-tRNA or added initiation factors. IF3mt has no effect on the formation of these complexes and cannot dissociate them once formed. These observations have lead to a new model for the function of IF3mt in mitochondrial translational initiation.