Romeo J M, Zusman D R
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
Mol Microbiol. 1992 Oct;6(20):2975-88. doi: 10.1111/j.1365-2958.1992.tb01756.x.
Myxococcus xanthus is a Gram-negative bacterium which has a complex life cycle that includes development (fruiting body formation). The gene for myxobacterial haemagglutinin, mbhA, is developmentally regulated and highly expressed. In this report we show that the mbhA mRNA is exceptionally stable for a prokaryotic organism, exhibiting a chemical half life (t1/2) of 150 min at 18 h of development. The mbhA mRNA was not stable in vegetatively growing cells nor was it stable when expressed in Escherichia coli. We have used site-directed mutagenesis of the mbhA gene to analyse some of the determinants which mediate the stability of the mbhA transcript. Sequences within the 3'-untranslated region (3'-UTR) were found to be crucial for mRNA stability. This region of mRNA can potentially form an extremely stable stem-loop structure immediately adjacent to the translational stop codon. A deletion within this region caused a 10-fold increase in the decay rate of the transcript. Furthermore, conditions which were associated with reduced mbhA translation or mutations that caused premature termination of translation drastically reduced mRNA stability even in the presence of the wild type 3'-UTR. These results suggest that a significant aspect of mbhA mRNA stability involves a synergistic interaction of the translational machinery with sequence elements within the 3'-UTR.
黄色粘球菌是一种革兰氏阴性细菌，具有复杂的生命周期，包括发育过程（子实体形成）。粘细菌血凝素基因mbhA受发育调控且高度表达。在本报告中，我们表明，mbhA mRNA对于原核生物而言异常稳定，在发育18小时时化学半衰期（t1/2）为150分钟。mbhA mRNA在营养生长的细胞中不稳定，在大肠杆菌中表达时也不稳定。我们利用mbhA基因的定点诱变来分析一些介导mbhA转录本稳定性的决定因素。发现3'-非翻译区（3'-UTR）内的序列对于mRNA稳定性至关重要。该mRNA区域可能紧邻翻译终止密码子形成极其稳定的茎环结构。该区域内的一个缺失导致转录本衰变率增加10倍。此外，与mbhA翻译减少相关的条件或导致翻译提前终止的突变，即使在存在野生型3'-UTR的情况下，也会大幅降低mRNA稳定性。这些结果表明，mbhA mRNA稳定性的一个重要方面涉及翻译机制与3'-UTR内序列元件的协同相互作用。
