Role of the single-stranded DNA-binding protein SsbB in pneumococcal transformation: maintenance of a reservoir for genetic plasticity.
Role of the single-stranded DNA-binding protein SsbB in pneumococcal transformation: maintenance of a reservoir for genetic plasticity.
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DOI：
10.1371/journal.pgen.1002156
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发表时间：
2011-06
期刊：
影响因子：
4.5
通讯作者：
Claverys JP
中科院分区：
文献类型：
--
作者：
Attaiech L;Olivier A;Mortier-Barrière I;Soulet AL;Granadel C;Martin B;Polard P;Claverys JP
细菌编码一种单链DNA（ssDNA）结合蛋白（SSB），对基因组的维持至关重要。在枯草芽孢杆菌和肺炎链球菌中，另一种SSB SsbB在遗传转化的感受态中唯一表达，但其确切作用一直不清楚。在这里，我们报告了我们的调查，涉及比较一个无效突变体（ssbB −）和一个C端截断（ssbBΔ7）的SsbB的。pneumoniae，后者的构建是因为SSB的酸性尾已经成为与伴侣蛋白相互作用的关键位点。我们提供的证据表明，SsbB直接保护内化的ssDNA。我们表明，SsbB是非常丰富的，可能允许的结合1.15 Mb的ssDNA（半个基因组当量），它参与到重组体的ssDNA的加工，并在高DNA浓度，它是至关重要的染色体转化，同时拮抗质粒转化。而后者的观察结果解释了一个长期的观察结果，即质粒转化在S。pneumoniae（与染色体转化相比），前者支持我们先前的建议，即SsbB创建ssDNA的储库，允许连续的重组循环。SsbBΔ7实现了储库功能，表明SsbB C-ter对于处理蛋白质以访问存储的ssDNA不是必需的。我们认为，SsbB的进化存在的理由和它的丰富性是维持这个水库，这有助于S的遗传可塑性。通过增加同一细胞中多个转化事件的可能性来抑制肺炎。自然的遗传转化可以弥补细菌有性繁殖的缺失，通过频繁的重组使基因多样化。在许多物种中，可转化性是一种短暂的性质，依赖于一种专门的膜相关机制，用于结合外源性双链DNA和内化从外源性DNA提取的单链DNA（ssDNA）片段。随后通过同源重组将内化的ssDNA物理整合到受体染色体中需要专用的胞质ssDNA加工蛋白。在这里，我们的文件中的角色，在模型中可转化的物种肺炎链球菌的这些处理蛋白，SsbB，一个paramount的SsbA的ssDNA结合蛋白在细菌中的基因组维护，这是唯一的表达在细胞中的基因转化能力。我们表明，SsbB是非常丰富的，可能允许的结合1.15 Mb的ssDNA（半个基因组当量），它参与到重组体的ssDNA的加工，它保护和稳定内化的ssDNA，并在高DNA浓度，它是至关重要的染色体转化，同时拮抗质粒转化。我们的结论是，SsbB创造了一个ssDNA的水库，大概允许在同一个细胞中的多个转换，和S。pneumoniae已经进化出SsbB以优化染色体转化，从而有助于其显著的遗传可塑性。
Bacteria encode a single-stranded DNA (ssDNA) binding protein (SSB) crucial for genome maintenance. In Bacillus subtilis and Streptococcus pneumoniae, an alternative SSB, SsbB, is expressed uniquely during competence for genetic transformation, but its precise role has been disappointingly obscure. Here, we report our investigations involving comparison of a null mutant (ssbB −) and a C-ter truncation (ssbBΔ7) of SsbB of S. pneumoniae, the latter constructed because SSBs' acidic tail has emerged as a key site for interactions with partner proteins. We provide evidence that SsbB directly protects internalized ssDNA. We show that SsbB is highly abundant, potentially allowing the binding of ∼1.15 Mb ssDNA (half a genome equivalent); that it participates in the processing of ssDNA into recombinants; and that, at high DNA concentration, it is of crucial importance for chromosomal transformation whilst antagonizing plasmid transformation. While the latter observation explains a long-standing observation that plasmid transformation is very inefficient in S. pneumoniae (compared to chromosomal transformation), the former supports our previous suggestion that SsbB creates a reservoir of ssDNA, allowing successive recombination cycles. SsbBΔ7 fulfils the reservoir function, suggesting that SsbB C-ter is not necessary for processing protein(s) to access stored ssDNA. We propose that the evolutionary raison d'être of SsbB and its abundance is maintenance of this reservoir, which contributes to the genetic plasticity of S. pneumoniae by increasing the likelihood of multiple transformation events in the same cell. Natural genetic transformation can compensate for the absence of sexual reproduction in bacteria, allowing genetic diversification by frequent recombination. In many species, transformability is a transient property relying on a specialized membrane-associated machinery for binding exogenous double-stranded DNA and internalization of single-stranded DNA (ssDNA) fragments extracted from exogenous DNA. Subsequent physical integration of internalized ssDNA into the recipient chromosome by homologous recombination requires dedicated cytosolic ssDNA–processing proteins. Here, we document the roles in the model transformable species Streptococcus pneumoniae of one of these processing proteins, SsbB, a paralogue of SsbA the ssDNA–binding protein essential for genome maintenance in bacteria, which is expressed uniquely in cells competent for genetic transformation. We show that SsbB is highly abundant, potentially allowing the binding of ∼1.15 Mb ssDNA (half a genome equivalent); that it participates in the processing of ssDNA into recombinants; that it protects and stabilizes internalized ssDNA; and that, at high DNA concentration, it is of crucial importance for chromosomal transformation whilst antagonizing plasmid transformation. We conclude that SsbB creates a reservoir of ssDNA, presumably allowing multiple transformations in the same cell, and that S. pneumoniae has evolved SsbB to optimize chromosomal transformation, thereby contributing to its remarkable genetic plasticity.
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DOI：
10.1073/pnas.252633399
发表时间：
2002-11-26
影响因子：
11.1
作者：
Kantake, N;Madiraju, MVVM;Kowalczykowski, C
通讯作者：
Kowalczykowski, C
影响因子：
3.2
作者：
Cartee, RT;Forsee, WT;Yother, J
通讯作者：
Yother, J
影响因子：
3.2
作者：
Lindner, C;Nijland, R;Kuipers, OP
通讯作者：
Kuipers, OP
影响因子：
4.5
作者：
Costes A;Lecointe F;McGovern S;Quevillon-Cheruel S;Polard P
通讯作者：
Polard P
影响因子：
3.6
作者：
Martin, B;Prudhomme, M;Claverys, JP
通讯作者：
Claverys, JP