Mutants of the RNA-processing enzyme RNase E reverse the extreme slow-growth phenotype caused by a mutant translation factor EF-Tu
Mutants of the RNA-processing enzyme RNase E reverse the extreme slow-growth phenotype caused by a mutant translation factor EF-Tu
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DOI：
10.1111/j.1365-2958.2008.06472.x
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发表时间：
2008-12-01
影响因子：
3.6
通讯作者：
Hughes, Diarmaid
中科院分区：
文献类型：
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作者：
Hammarloef, Disa L.;Hughes, Diarmaid
具有突变EF-Tu（Gln 125 Arg）的肠道沙门氏菌具有低水平的EF-Tu、降低的蛋白质合成速率和极慢的生长速率。选择了80个独立的抑制突变，恢复正常生长。在某些情况下（n = 7），抑制是由于tufA中的突变，但令人惊讶的是，在大多数情况下（n = 73），抑制是由于编码RNase E的基因rne中的突变。这些rne突变单独对生长速度只有适度的影响。在rne中分离出50种不同的抑制突变，它们都位于或靠近RNase E的N-末端核酸内切酶的一半。几种mRNA的稳态水平较低的突变体tuf菌株，但恢复到野生型水平的tuf-rne双突变体。相反，mRNA的半衰期不受tuf突变的影响。我们提出了一个模型，其中tuf突变导致核糖体以下RNA聚合酶暂停，可能是在一个密码子特异性的方式，暴露未屏蔽的新生信息RNase E切割。通过增加EF-Tu活性或降低RNase E活性可以恢复正常生长速率。因此，RNase E被认为在mRNA生命的两个不同阶段起作用：早期，在新生的转录物上;晚期，在完整的mRNA上。
Salmonella enterica with mutant EF-Tu (Gln125Arg) has a low level of EF-Tu, a reduced rate of protein synthesis and an extremely slow growth rate. Eighty independent suppressor mutations were selected that restored normal growth. In some cases (n = 7) suppression was due to mutations in tufA but, surprisingly, in most cases (n = 73) to mutations in rne, the gene coding for RNase E. These rne mutations alone had only modest effects on growth rate. Fifty different suppressor mutations were isolated in rne, all located in or close to the N-terminal endonucleolytic half of RNase E. Steady state levels of several mRNAs were lower in the mutant tuf strain but restored to wild-type levels in the tuf-rne double mutant. In contrast, the half-lives of mRNAs were unaffected by the tuf mutation. We propose a model where the tuf mutation causes the ribosome following RNA polymerase to pause, possibly in a codon-specific manner, exposing unshielded nascent message to RNase E cleavage. Normal growth rate can be restored by increasing EF-Tu activity or by reducing RNase E activity. Accordingly, RNase E is suggested to act at two distinct stages in the life of mRNA: early, on the nascent transcript; late, on the complete mRNA.