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首页> 外文期刊>Journal of Molecular Biology >Molecular clocks reduce plasmid loss rates: the R1 case.
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Molecular clocks reduce plasmid loss rates: the R1 case.

机译：分子钟降低了质粒丢失率：R1病例。

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摘要

Plasmids control their replication so that the replication frequency per plasmid copy responds to the number of plasmid copies per cell. High sensitivity amplification in replication response to copy number deviations generally reduces variation in copy numbers between different single cells, thereby reducing the plasmid loss rate in a cell population. However, experiments show that plasmid R1 has a gradual, insensitive replication control predicting considerable copy number variation between single cells. The critical step in R1 copy number control is regulation of synthesis of a rate-limiting cis-acting replication protein, RepA. De novo synthesis of a large number of RepA molecules is required for replication, suggesting that copy number control is exercised at multiple steps. In this theoretical kinetic study we analyse R1 multistep copy number control and show that it results in the insensitive replication response found experimentally but that it at the same time effectively prohibits the existence of only one plasmid copy in a dividing cell. In combination with the partition system of R1, this can lead to very high segregational stability. The R1 control mechanism is compared to the different multistep copy number control of plasmid ColE1 that is based on conventional sensitivity amplification. This implies that while copy number control for ColE1 efficiently corrects for fluctuations that have already occurred, R1 copy number control prevents their emergence in cells that by chance start their cycle with only one plasmid copy. We also discuss how regular, clock-like, behaviour of single plasmid copies becomes hidden in experiments probing collective properties of a population of plasmid copies because the individual copies are out of phase. The model is formulated using master equations, taking a stochastic approach to regulation, but the mathematical formalism is kept to a minimum and the model is simplified to its bare essence. This simplicity makes it possible to extend the analysis to other replicons with similar design principles. Copyright 2000 Academic Press.
机译：质粒控制其复制，以使每个质粒拷贝的复制频率响应每个细胞的质粒拷贝数。对拷贝数偏差的复制响应中的高灵敏度扩增通常会减少不同单细胞之间拷贝数的变化，从而降低细胞群中质粒的丢失率。但是，实验表明，质粒R1具有渐进的，不灵敏的复制控制，可预测单个细胞之间的拷贝数差异很大。 R1拷贝数控制中的关键步骤是调节限速顺式复制蛋白RepA的合成。从头合成大量RepA分子对于复制是必需的，这表明复制数控制是在多个步骤中进行的。在这项理论动力学研究中，我们分析了R1多步复制数控制，并表明它导致了实验发现的不敏感复制反应，但同时却有效地阻止了分裂细胞中仅存在一个质粒复制。与R1的分隔系统结合使用，可以导致很高的隔离稳定性。将R1控制机制与基于常规灵敏度扩增的质粒ColE1的不同多步复制数控制进行了比较。这意味着尽管对ColE1的拷贝数控制有效地纠正了已经发生的波动，但R1拷贝数控制可防止它们出现在偶然以仅一个质粒拷贝开始其循环的细胞中。我们还讨论了单个质粒拷贝的规则，类似时钟的行为如何在探测质粒拷贝群体的集体特性的实验中被隐藏了，因为单个拷贝是异相的。该模型是使用主方程式制定的，采用了一种随机方法进行调节，但是数学形式主义保持在最低限度，并且该模型被简化为其本质。这种简单性使得可以将分析扩展到具有类似设计原理的其他复制子。版权所有2000学术出版社。

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