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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Translation arrest of SecM is essential for the basal and regulated expression of SecA
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Translation arrest of SecM is essential for the basal and regulated expression of SecA

机译：SecM的翻译逮捕对于SecA的基础表达和调控表达至关重要

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The SecM protein of Escherichia coli contains an arrest sequence (F(150)XXXXWlXXXXGIRAGP(166)), which interacts with the ribosomal exit tunnel to halt translation elongation beyond Pro-166. This inhibition is reversed by active export of the nascent SecM chain. Here, we studied the physiological roles of SecM. Arrest-alleviating mutations in the arrest sequence reduced the expression of secA, a downstream gene on the same mRNA. Among such mutations, the arrest-abolishing P166A substitution mutation on the chromosomal secM gene proved lethal unless the mutant cells are complemented with excess SecA. Whereas secretion defect due either to azide addition, a secY mutation, or low temperature leads to up-regulated SecA biosynthesis, this regulation was lost by a secM mutation, which synergistically retarded growth of cells with lowered secretion activity. Finally, an arrest-alleviating rRNA mutation affecting the constricted part of the exit tunnel lowered the basal level of SecA as well as its secretion defect-induced upregulation. Thus, the arrest sequence of SecM has at least two roles in SecA translation. First, the transient elongation arrest in normal cells is required for the synthesis of SecA at levels sufficient to support cell growth. Second, the prolonged SecM elongation arrest under conditions of unfavorable protein secretion is required for the enhanced expression of SecA to cope with such conditions.
机译：大肠杆菌的SecM蛋白包含一个逮捕序列（F（150）XXXXW1XXXXGIRAGP（166）），该序列与核糖体出口通道相互作用，以阻止翻译延伸超过Pro-166。通过新生SecM链的主动输出可以逆转这种抑制作用。在这里，我们研究了SecM的生理作用。逮捕序列中减轻逮捕的突变减少了secA的表达，secA是同一mRNA上的下游基因。在此类突变中，除非突变细胞补充了过量的SecA，否则染色体secM基因上破坏逮捕的P166A替代突变被证明具有致命性。而由于叠氮化物添加，secY突变或低温导致的分泌缺陷会导致SecA生物合成上调，而secM突变会失去这种调节，从而协同抑制分泌活性降低的细胞生长。最后，影响出口通道狭窄部分的减轻缓解的rRNA突变降低了SecA的基础水平及其分泌缺陷引起的上调。因此，SecM的阻滞序列在SecA翻译中至少具有两个作用。首先，在正常细胞中短暂的伸长停滞对于合成SecA而言是必需的，其水平足以支持细胞生长。其次，为了增强SecA的表达来应对这种情况，需要在蛋白质分泌不利的条件下延长SecM的延长阻滞。

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