Abo T, Inada T, Ogawa K, Aiba H
Division of Biological Science, Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan.
EMBO J. 2000 Jul 17;19(14):3762-9. doi: 10.1093/emboj/19.14.3762.
SsrA RNA of Escherichia coli, also known as 10Sa RNA or tmRNA, acts both as tRNA and mRNA when ribosomes are paused at the 3' end of an mRNA lacking a stop codon. This process, referred to as trans-translation, leads to the addition of a short peptide tag to the C-terminus of the incomplete nascent polypeptide. The tagged polypeptide is then degraded by C-terminal-specific proteases. Here, we focused on endogenous targets for the SsrA system and on a potential regulatory role of SsrA RNA. First, we show that trans-translation events occur frequently in normally growing E. COLI: cells. More specifically, we report that the lacI mRNA encoding Lac repressor (LacI) is a specific natural target for trans-translation. The binding of LacI to the lac operators results in truncated lacI mRNAs that are, in turn, recognized by the SsrA system. The SsrA-mediated tagging and proteolysis of LacI appears to play a role in cellular adaptation to lactose availability by supporting a rapid induction of lac operon expression.
大肠杆菌的SsrA RNA，也被称为10Sa RNA或tmRNA，当核糖体在缺乏终止密码子的mRNA的3'末端暂停时，它同时充当tRNA和mRNA。这个过程被称为反式翻译，导致在不完整的新生多肽的C末端添加一个短肽标签。然后，被标记的多肽被C末端特异性蛋白酶降解。在这里，我们关注SsrA系统的内源性靶标以及SsrA RNA的潜在调节作用。首先，我们表明反式翻译事件在正常生长的大肠杆菌细胞中频繁发生。更具体地说，我们报告编码Lac阻遏物（LacI）的lacI mRNA是反式翻译的一个特定天然靶标。LacI与lac操纵子的结合导致截短的lacI mRNA，进而被SsrA系统识别。SsrA介导的LacI标记和蛋白水解似乎通过支持lac操纵子表达的快速诱导在细胞对乳糖可用性的适应中发挥作用。
