Govantes F, Andújar E, Santero E
Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Ap. 1095, 41080-Sevilla, Spain.
EMBO J. 1998 Apr 15;17(8):2368-77. doi: 10.1093/emboj/17.8.2368.
The nifLA operon of Klebsiella pneumoniae encodes the sensor-activator pair involved in the regulation of other nif genes. Balanced synthesis of both proteins, which is required for correct regulation, is achieved by coupling translation of nifA to that of nifL. The mechanism of translational coupling at the nifLA operon was analysed using a specialized ribosome system, and the effect of substituting the natural Shine-Dalgarno of nifL or nifA for specialized Shine-Dalgarno sequences was determined. Our results indicate that translational coupling occurs in this operon by a reinitiation mechanism. Additionally, reinitiation at the nifA can happen even in the absence of good Shine-Dalgarno recognition by the reinitiating ribosome, although its efficiency is lower. The effect of a putative translational enhancer sequence (downstream box) on translational coupling efficiency was also determined. Mutations that reduce the homology of the putative downstream box to the consensus had only a minor effect on nifA translation by wild-type ribosomes. However, they had a significant effect on nifA translation by specialized ribosomes, suggesting that recognition of the downstream box may compensate inefficient ribosomal interactions with the Shine-Dalgarno sequence.
肺炎克雷伯菌的nifLA操纵子编码参与其他nif基因调控的传感器-激活剂对。通过将nifA的翻译与nifL的翻译偶联，实现了正确调控所需的两种蛋白质的平衡合成。使用专门的核糖体系统分析了nifLA操纵子处的翻译偶联机制，并确定了用专门的Shine-Dalgarno序列替代nifL或nifA的天然Shine-Dalgarno的效果。我们的结果表明，该操纵子中的翻译偶联是通过重新起始机制发生的。此外，即使重新起始的核糖体对Shine-Dalgarno的识别不佳，nifA处的重新起始也可能发生，尽管其效率较低。还确定了推定的翻译增强子序列（下游框）对翻译偶联效率的影响。降低推定的下游框与共有序列同源性的突变对野生型核糖体的nifA翻译只有轻微影响。然而，它们对专门核糖体的nifA翻译有显著影响，这表明对下游框的识别可能补偿核糖体与Shine-Dalgarno序列的低效相互作用。
