Krishnamurthi Revathy, Ghosh Swagatha, Khedkar Supriya, Seshasayee Aswin Sai Narain
Shanmuga Arts, Science, Technology & Research Academy, Thanjavur, Tamil Nadu, India.
National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore, India.
mSphere. 2017 Nov 22;2(6). doi: 10.1128/mSphere.00392-17. eCollection 2017 Nov-Dec.
Horizontal gene transfer is a major driving force behind the genomic diversity seen in prokaryotes. The cryptic prophage in K-12 carries the gene for a putative transcription factor RacR, whose deletion is lethal. We have shown that the essentiality of in K-12 is attributed to its role in transcriptionally repressing toxin gene(s) called and , which are adjacent to and coded divergently to . Transcription factors in the bacterium are rarely essential, and when they are essential, they are largely toxin-antitoxin systems. While studying transcription factors encoded in horizontally acquired regions in , we realized that the protein RacR, a putative transcription factor encoded by a gene on the prophage, is an essential protein. Here, using genetics, biochemistry, and bioinformatics, we show that its essentiality derives from its role as a transcriptional repressor of the and genes, whose products are toxic to the cell. Unlike type II toxin-antitoxin systems in which transcriptional regulation involves complexes of the toxin and antitoxin, repression by RacR is sufficient to keep transcriptionally silent.
水平基因转移是原核生物基因组多样性背后的主要驱动力。K-12中的隐蔽原噬菌体携带一种假定转录因子RacR的基因，其缺失是致命的。我们已经表明，K-12中该基因的必需性归因于其在转录抑制称为 和 的毒素基因方面的作用，这些毒素基因与 相邻且编码方向相反。细菌中的转录因子很少是必需的，当它们是必需的时候，它们大多是毒素-抗毒素系统。在研究 中水平获得区域编码的转录因子时，我们意识到蛋白质RacR，一种由原噬菌体上的基因编码的假定转录因子，是一种必需蛋白质。在这里，我们使用遗传学、生物化学和生物信息学表明，其必需性源于它作为 和 基因转录阻遏物的作用，其产物对细胞有毒。与II型毒素-抗毒素系统不同，在II型毒素-抗毒素系统中，转录调控涉及毒素和抗毒素的复合物，RacR的阻遏足以使 转录沉默。
