Department of Physiology and Molecular Biophysics, Virginia Commonwealth University, Richmond, VA, USA.
BMC Microbiol. 2012 Oct 24;12:244. doi: 10.1186/1471-2180-12-244.
The KsgA methyltransferase has been conserved throughout evolution, methylating two adenosines in the small subunit rRNA in all three domains of life as well as in eukaryotic organelles that contain ribosomes. Understanding of KsgA's important role in ribosome biogenesis has been recently expanded in Escherichia coli; these studies help explain why KsgA is so highly conserved and also suggest KsgA's potential as an antimicrobial drug target.
We have analyzed KsgA's contribution to ribosome biogenesis and cell growth in Staphylococcus aureus. We found that deletion of ksgA in S. aureus led to a cold-sensitive growth phenotype, although KsgA was not as critical for ribosome biogenesis as it was shown to be in E. coli. Additionally, the ksgA knockout strain showed an increased sensitivity to aminoglycoside antibiotics. Overexpression of a catalytically inactive KsgA mutant was deleterious in the knockout strain but not the wild-type strain; this negative phenotype disappeared at low temperature.
This work extends the study of KsgA, allowing comparison of this aspect of ribosome biogenesis between a Gram-negative and a Gram-positive organism. Our results in S. aureus are in contrast to results previously described in E. coli, where the catalytically inactive protein showed a negative phenotype in the presence or absence of endogenous KsgA.
KsgA 甲基转移酶在进化过程中一直被保守，它甲基化了所有三个生命领域以及包含核糖体的真核细胞器中小亚基 rRNA 中的两个腺苷。对大肠杆菌中 KsgA 在核糖体生物发生中的重要作用的理解最近得到了扩展；这些研究有助于解释为什么 KsgA 如此高度保守，也表明 KsgA 作为一种抗菌药物靶标的潜力。
我们分析了 KsgA 在金黄色葡萄球菌中对核糖体生物发生和细胞生长的贡献。我们发现，尽管 KsgA 对核糖体生物发生的重要性不如在大肠杆菌中那样显著，但在金黄色葡萄球菌中敲除 ksgA 会导致冷敏感生长表型。此外，ksgA 敲除株对氨基糖苷类抗生素表现出更高的敏感性。在敲除株中过表达无催化活性的 KsgA 突变体是有害的，但在野生型株中则不然；这种负表型在低温下消失。
这项工作扩展了对 KsgA 的研究，允许在革兰氏阴性和革兰氏阳性生物体之间比较核糖体生物发生的这一方面。我们在金黄色葡萄球菌中的结果与之前在大肠杆菌中描述的结果形成对比，在大肠杆菌中，无催化活性的蛋白质在存在或不存在内源性 KsgA 的情况下表现出负表型。
