Translation arrest of SecM is essential for the basal and regulated expression of SecA
Translation arrest of SecM is essential for the basal and regulated expression of SecA
复制标题
DOI：
10.1073/pnas.0404907101
复制
发表时间：
2004-08-17
影响因子：
11.1
通讯作者：
Ito, K
中科院分区：
文献类型：
--
作者：
Murakami, A;Nakatogawa, H;Ito, K
大肠杆菌的SECM蛋白含有一个阻止序列(F(150)XXXXWlXXXXGIRAGP(166))，它与核糖体出口隧道相互作用，阻止Pro-166以外的翻译延伸。这种抑制作用被新生的SECM链的活跃输出所逆转。在这里，我们研究了SECM的生理作用。停滞序列中的停滞缓解突变减少了SecA的表达，SecA是同一mRNA上的下游基因。在这些突变中，染色体上SECM基因上的P166A替代突变被证明是致命的，除非突变细胞被过量的SecA补充。然而，由于叠氮添加、Secy突变或低温导致的分泌缺陷导致SecA生物合成上调，但这种调节被SECM突变所丢失，该突变协同抑制分泌活性降低的细胞的生长。最后，影响出口通道狭窄部分的缓解停滞的rRNA突变降低了SecA的基础水平，以及它的分泌缺陷诱导的上调。因此，SECM的逮捕顺序在SECA翻译中至少有两个作用。首先，正常细胞中的短暂伸长停止是合成足够支持细胞生长的SecA所必需的。其次，在不利于蛋白质分泌的条件下延长SECM的伸长停滞是SECA增强表达以应对这种条件所必需的。
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.