Programmed protection of foreign DNA from restriction allows pathogenicity island exchange during pneumococcal transformation.
Programmed protection of foreign DNA from restriction allows pathogenicity island exchange during pneumococcal transformation.
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DOI：
10.1371/journal.ppat.1003178
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发表时间：
2013-02
期刊：
影响因子：
6.7
通讯作者：
Claverys JP
中科院分区：
文献类型：
--
作者：
Johnston C;Martin B;Granadel C;Polard P;Claverys JP
在细菌中，转化和限制修饰（R-M）系统发挥潜在的拮抗作用。前者被认为是性的一种形式，依赖于内化的外来DNA来创造遗传多样性，而后者则降解外来DNA以保护免受噬菌体的攻击。人类病原体肺炎链球菌是可转化的，并且具有两个R-M系统Dpn I和Dpn II中的任一个，其分别限制甲基化或未甲基化的双链（ds）DNA。S.肺炎DpnII菌株具有DpnM和第二甲基化酶DpnA，DpnM使dsDNA甲基化以保护其免受DpnII限制，DpnA在遗传转化的感受态期间被诱导，并且不寻常的是它使单链（ss）DNA甲基化。DpnA暂时被认为是保护内化质粒免受DpnII限制的作用，但根据最近的结果，这似乎不太可能，因为肺炎球菌转化并没有进化到有利于质粒交换。在这里，我们验证了另一种假设，表明DpnA在保护内化的外源DNA中起着至关重要的作用，使交换的致病性岛屿和更普遍的可变区之间的肺炎球菌分离株。我们发现，21.7 kb的异源区域的转化减少了超过4个对数的dpnA突变细胞，并提供证据表明，在竞争期间的特异性诱导dpnA是至关重要的充分保护。我们建议，限制酶/ssDNA-甲基化酶偶联到能力调节子的整合保持保护免受噬菌体攻击，同时使交换pathogenicicy岛。DpnA的这种保护作用可能对肺炎球菌毒力特别重要，因为它允许DpnII菌株通过DpnI胶囊位点的整合而自由变异胶囊血清型，从而有助于记录肺炎球菌从基于胶囊的疫苗中逃逸。总的来说，这一发现是第一个积极促进S遗传多样性的机制的证据。肺炎通过程序化保护和外源DNA的掺入。自然遗传转化可以弥补细菌有性繁殖的缺失，允许通过重组实现遗传多样化。它通过由外源性双链（ds）DNA底物产生的单链（ss）DNA片段的内化进行，所述单链（ss）DNA片段通过同源性并入基因组中。另一方面，限制修饰（R-M）系统，保护细菌免受噬菌体的攻击，通过降解入侵的外源DNA，潜在地拮抗转化。大约一半的天然可转化物种和人类病原体肺炎链球菌的菌株具有限制未甲基化dsDNA的R-M系统Dpn II。DpnII菌株具有DpnA，这是不寻常的，因为它甲基化ssDNA。在这里，我们表明，DpnA起着至关重要的作用，在保护内化的异源转化的ssDNA，防止复制后破坏DpnII的转化产生的染色体整合的异源DNA凭借侧翼同源性。DpnA的这种保护作用对于DpnII菌株从非DpnII来源获得致病性岛（如胶囊位点）特别重要，这可能通过从基于胶囊的疫苗中逃逸而导致肺炎球菌毒力。总的来说，这一发现是第一个积极促进S遗传多样性的机制的证据。肺炎通过主动保护和外源DNA的掺入。
In bacteria, transformation and restriction-modification (R-M) systems play potentially antagonistic roles. While the former, proposed as a form of sexuality, relies on internalized foreign DNA to create genetic diversity, the latter degrade foreign DNA to protect from bacteriophage attack. The human pathogen Streptococcus pneumoniae is transformable and possesses either of two R-M systems, DpnI and DpnII, which respectively restrict methylated or unmethylated double-stranded (ds) DNA. S. pneumoniae DpnII strains possess DpnM, which methylates dsDNA to protect it from DpnII restriction, and a second methylase, DpnA, which is induced during competence for genetic transformation and is unusual in that it methylates single-stranded (ss) DNA. DpnA was tentatively ascribed the role of protecting internalized plasmids from DpnII restriction, but this seems unlikely in light of recent results establishing that pneumococcal transformation was not evolved to favor plasmid exchange. Here we validate an alternative hypothesis, showing that DpnA plays a crucial role in the protection of internalized foreign DNA, enabling exchange of pathogenicity islands and more generally of variable regions between pneumococcal isolates. We show that transformation of a 21.7 kb heterologous region is reduced by more than 4 logs in dpnA mutant cells and provide evidence that the specific induction of dpnA during competence is critical for full protection. We suggest that the integration of a restrictase/ssDNA-methylase couplet into the competence regulon maintains protection from bacteriophage attack whilst simultaneously enabling exchange of pathogenicicy islands. This protective role of DpnA is likely to be of particular importance for pneumococcal virulence by allowing free variation of capsule serotype in DpnII strains via integration of DpnI capsule loci, contributing to the documented escape of pneumococci from capsule-based vaccines. Generally, this finding is the first evidence for a mechanism that actively promotes genetic diversity of S. pneumoniae through programmed protection and incorporation of foreign DNA. Natural genetic transformation can compensate for the absence of sexual reproduction in bacteria, allowing genetic diversification by recombination. It proceeds through the internalization of single stranded (ss) DNA fragments created from an exogenous double stranded (ds) DNA substrate, which are incorporated into the genome by homology. On the other hand, restriction-modification (R-M) systems, which protect bacteria from bacteriophage attack by degrading invading foreign DNA, potentially antagonize transformation. About half of the strains of the naturally transformable species and human pathogen Streptococcus pneumoniae possess an R-M system, DpnII, restricting unmethylated dsDNA. DpnII strains possess DpnA which is unusual in that it methylates ssDNA. Here we show that DpnA plays a crucial role in the protection of internalized heterologous transforming ssDNA, preventing the post-replicative destruction by DpnII of transformants produced by chromosomal integration of heterogolous DNA by virtue of flanking homology. This protective role of DpnA is of particular importance for acquisition of pathogenicity islands, such as capsule loci, from non-DpnII origin by DpnII strains, likely contributing to pneumococcal virulence via escape from capsule-based vaccines. Generally, this finding is the first evidence for a mechanism that actively promotes genetic diversity of S. pneumoniae through active protection and incorporation of foreign DNA.
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影响因子：
4.5
作者：
Attaiech L;Olivier A;Mortier-Barrière I;Soulet AL;Granadel C;Martin B;Polard P;Claverys JP
通讯作者：
Claverys JP
影响因子：
6.7
作者：
Brueggemann, Angela B.;Pai, Rekha;Beall, Bernard
通讯作者：
Beall, Bernard
DOI：
10.1126/science.1165771
发表时间：
2008-12-19
期刊：
Science (New York, N.Y.)
影响因子：
--
作者：
Marraffini LA;Sontheimer EJ
通讯作者：
Sontheimer EJ
影响因子：
3.2
作者：
Lee, MS;Morrison, DA
通讯作者：
Morrison, DA
DOI：
10.1073/pnas.86.23.9223
发表时间：
1989-12-01
影响因子：
11.1
作者：
CERRITELLI, S;SPRINGHORN, SS;LACKS, SA
通讯作者：
LACKS, SA