Multicopy plasmid stability: Revisiting the dimer catastrophe
Multicopy plasmid stability: Revisiting the dimer catastrophe
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DOI：
10.1016/j.jtbi.2011.09.006
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发表时间：
2011-12-21
影响因子：
2
通讯作者：
Summers, D. K.
中科院分区：
文献类型：
--
作者：
Field, C. M.;Summers, D. K.
在这项研究中，我们构建了细菌多拷贝质粒ColE1在指数生长细胞群体中的复制和分布的随机模拟。假设ColE1在子细胞分裂时随机分布，因此拷贝数是质粒丢失的关键决定因素。高拷贝数受到质粒二聚体的威胁，其最初由同源重组产生，并在称为“二聚体灾难”的过程中通过复制积累。Summers等人（1993）模拟了这一过程，并证明二聚体的积累受到它们施加给宿主的代谢负荷的限制。ColE1也编码cer位点，宿主编码的蛋白质通过位点特异性重组将二聚体转化为单体。cer位点还编码一种调节性RNA Rcd，其从质粒二聚体合成触发一个延迟细胞分裂的检查点，可能为二聚体的分解留出了足够的时间。在这里，我们通过将拷贝数方差与质粒复制的随机模型相结合，开发了原始的二聚体突变模型。我们证明，当二聚体分辨率较慢时，Rcd检查点是必要的。我们的研究结果表明，与单体相比，二聚体过度复制，这表明它们增加代谢负荷的机制。我们发现二聚体对质粒稳定性的影响明显小于原始模型所建议的严重程度。因此，我们提出二聚体分解和Rcd检查点的主要作用是减少质粒在重组宿主中的代谢负担，而不是确保质粒的稳定性。(C) 2011 Elsevier Ltd.版权所有。
In this study, we have constructed a stochastic simulation of the replication and distribution of the bacterial multicopy plasmid ColE1 in a population of exponentially growing cells. It is assumed that ColE1 is randomly distributed between daughter cells at division such that copy number is a critical determinant of plasmid loss. High copy number is threatened by plasmid dimers, which arises initially by homologous recombination and accumulate by replication in a process known as the 'dimer catastrophe'. Summers et al. (1993) modelled this process and demonstrated that the accumulation of dimers is limited by the metabolic load that they exert on their hosts. ColE1 also encodes the cer site, at which host-encoded proteins act to convert dimers to monomers by site-specific recombination. The cer site also encodes a regulatory RNA, Rcd, whose synthesis from plasmid dimers triggers a checkpoint that delays cell division, presumably allowing sufficient time for dimer resolution. Here we have developed the original dimer catastrophe model by incorporating copy number variance with a stochastic model of plasmid replication. We demonstrate that the Rcd checkpoint is necessary when the rate of dimer resolution is slow. Our results indicate that dimers over-replicate compared to monomers, suggesting a mechanism for their increased metabolic load. We find that the effect of dimers on plasmid stability is significantly less severe than suggested by the original model. Consequently, we propose that the primary role of dimer resolution and the Rcd checkpoint is to reduce the metabolic burden imposed by the plasmid in a recombinogenic host, rather than to ensure plasmid stability. (C) 2011 Elsevier Ltd. All rights reserved.