Biebricher C K, Eigen M, Gardiner W C
Biochemistry. 1985 Nov 5;24(23):6550-60. doi: 10.1021/bi00344a037.
The process of Darwinian selection in the self-replication of single-stranded RNA by Q beta replicase was investigated by analytical and computer-simulation methods. For this system, the relative population change of the competing species was found to be a useful definition of selection value, calculable from measurable kinetic parameters and concentrations of each species. Critical differences in the criteria for selection were shown to pertain for replicase/RNA ratios greater than or less than 1, for the case that formation of double-stranded RNA occurs and when comparisons are made of closed with open systems. At a large excess of enzyme, RNA species grow exponentially without interfering with each other, and selection depends only on the fecundity of the species, i.e., their overall replication rates. For RNA concentrations greater than the replicase concentration, the selection of species is governed by their abilities to compete for enzyme. Under conditions where formation of double strands occurs, competition leads to a coexistence of the species; the selection values vanish, and the concentration ratios depend only on the template binding and double-strand formation rates. The approach to coexistence is rapid, because when its competitors are in a steady state, a species present in trace amount is amplified exponentially. When formation of hybrid double strands occurs at a substantial rate, coexistence of hybridizing species is essentially limited to cases where the formation rate of heterologous double strands is smaller than the geometric mean of the formation rates of the homologous double strands. At limiting cases, e.g. in the steady states, simple analytical expressions for the main aspects of the selection process were found. Experimental data support the analytical expressions and the simulations.
通过分析和计算机模拟方法研究了Qβ复制酶在单链RNA自我复制过程中的达尔文选择过程。对于该系统，竞争物种的相对种群变化被发现是选择值的一个有用定义，可根据每种物种的可测量动力学参数和浓度来计算。结果表明，对于大于或小于1的复制酶/RNA比率、双链RNA形成的情况以及封闭系统与开放系统的比较，选择标准存在关键差异。在酶大量过量的情况下，RNA物种呈指数增长且互不干扰，选择仅取决于物种的繁殖力，即它们的总体复制速率。当RNA浓度大于复制酶浓度时，物种的选择取决于它们竞争酶的能力。在双链形成的条件下，竞争导致物种共存；选择值消失，浓度比仅取决于模板结合和双链形成速率。共存的过程很快，因为当竞争者处于稳定状态时，微量存在的物种会呈指数扩增。当杂交双链的形成速率很大时，杂交物种的共存基本上仅限于异源双链的形成速率小于同源双链形成速率的几何平均值的情况。在极限情况下，例如在稳定状态下，找到了选择过程主要方面的简单解析表达式。实验数据支持这些解析表达式和模拟结果。
