Davis B K
Proc Natl Acad Sci U S A. 1979 May;76(5):2288-92. doi: 10.1073/pnas.76.5.2288.
The transmission of complexity during DNA replication has been investigated to clarify the significance of this molecular property in a deterministic process. Complexity was equated with the amount of randomness within an ordered molecular structure and measured by the entropy of a posteriori probabilities for discrete (monomer sequences, atomic bonds) and continuous (torsion angle sequences) structural parameters in polynucleotides, proteins, and ligand molecules. A theoretical analysis revealed that sequence complexity decreases during transmission from DNA to protein. It was also found that sequence complexity limits the attainable complexity in the folding of a polypeptide chain and that a protein cannot interact with a ligand moiety of higher complexity. The analysis indicated, furthermore, that in any deterministic molecular process a cause possesses more complexity than its effect. This outcome broadly complies with Curie's symmetry principle. Results from an analysis of an extensive set of experimental data are presented; they corroborate these findings. It is suggested, therefore, that complexity governs the direction of order-order molecular transformations. Two biological implications are (i) replication of DNA in a stepwise, repetitive manner by a polymerase appears to be a necessary consequence of structural constraints imposed by complexity, and (ii) during evolution, increases in complexity had to involve a nondeterministic mechanism. This latter requirement apparently applied also to development of the first replicating system on earth.
为了阐明这种分子特性在一个确定性过程中的重要性，人们对DNA复制过程中复杂性的传递进行了研究。复杂性被等同于有序分子结构内的随机量，并通过多核苷酸、蛋白质和配体分子中离散（单体序列、原子键）和连续（扭转角序列）结构参数的后验概率熵来衡量。理论分析表明，从DNA到蛋白质的传递过程中序列复杂性降低。还发现序列复杂性限制了多肽链折叠中可达到的复杂性，并且蛋白质不能与更高复杂性的配体部分相互作用。此外，分析表明，在任何确定性分子过程中，原因比其结果具有更多的复杂性。这一结果大致符合居里对称原理。给出了对大量实验数据的分析结果；它们证实了这些发现。因此，有人提出复杂性决定了有序-有序分子转变的方向。两个生物学意义是：（i）聚合酶以逐步、重复的方式复制DNA似乎是复杂性所施加的结构限制的必然结果，以及（ii）在进化过程中，复杂性的增加必须涉及一种非确定性机制。后一个要求显然也适用于地球上第一个复制系统的发展。
