Pandey Deo Prakash, Gerdes Kenn
Department of Biochemistry and Molecular Biology, University of Southern Denmark DK-5230 Odense M, Denmark.
Nucleic Acids Res. 2005 Feb 17;33(3):966-76. doi: 10.1093/nar/gki201. Print 2005.
Prokaryotic chromosomes code for toxin-antitoxin (TA) loci, often in multiple copies. In E.coli, experimental evidence indicates that TA loci are stress-response elements that help cells survive unfavorable growth conditions. The first gene in a TA operon codes for an antitoxin that combines with and neutralizes a regulatory 'toxin', encoded by the second gene. RelE and MazF toxins are regulators of translation that cleave mRNA and function, in interplay with tmRNA, in quality control of gene expression. Here, we present the results from an exhaustive search for TA loci in 126 completely sequenced prokaryotic genomes (16 archaea and 110 bacteria). We identified 671 TA loci belonging to the seven known TA gene families. Surprisingly, obligate intracellular organisms were devoid of TA loci, whereas free-living slowly growing prokaryotes had particularly many (38 in Mycobacterium tuberculosis and 43 in Nitrosomonas europaea). In many cases, TA loci were clustered and closely linked to mobile genetic elements. In the most extreme of these cases, all 13 TA loci of Vibrio cholerae were bona fide integron elements located in the V.cholerae mega-integron. These observations strongly suggest that TA loci are mobile cassettes that move frequently within and between chromosomes and also lend support to the hypothesis that TA loci function as stress-response elements beneficial to free-living prokaryotes.
原核生物染色体编码毒素 - 抗毒素（TA）位点，通常有多个拷贝。在大肠杆菌中，实验证据表明TA位点是应激反应元件，有助于细胞在不利的生长条件下存活。TA操纵子中的第一个基因编码一种抗毒素，它与第二个基因编码的调节性“毒素”结合并使其失活。RelE和MazF毒素是翻译调节因子，它们切割mRNA并与tmRNA相互作用，在基因表达的质量控制中发挥作用。在这里，我们展示了对126个完全测序的原核生物基因组（16个古细菌和110个细菌）进行TA位点详尽搜索的结果。我们鉴定出属于七个已知TA基因家族的671个TA位点。令人惊讶的是，专性细胞内生物没有TA位点，而自由生活的缓慢生长的原核生物则特别多（结核分枝杆菌中有38个，欧洲亚硝化单胞菌中有43个）。在许多情况下，TA位点聚集在一起并与移动遗传元件紧密相连。在最极端的情况下，霍乱弧菌的所有13个TA位点都是位于霍乱弧菌超级整合子中的真正整合子元件。这些观察结果强烈表明TA位点是可移动的基因盒，它们经常在染色体内和染色体之间移动，也支持了TA位点作为对自由生活的原核生物有益的应激反应元件的假说。
