Abstract
DNA in all living systems shares common properties that are remarkably well suited to its function, suggesting refinement by evolution. However, DNA also shares some counter-intuitive properties which confer no obvious benefit, such as strand directionality and anti-parallel strand orientation, which together result in the complicated lagging strand replication. The evolutionary dynamics that led to these properties of DNA remain unknown but their universality suggests that they confer as yet unknown selective advantage to DNA. In this article, we identify an evolutionary advantage of anti-parallel strand orientation of duplex DNA, within a given set of plausible premises. The advantage stems from the increased rate of replication, achieved by dividing the DNA into predictable, independently and simultaneously replicating segments, as opposed to sequentially replicating the entire DNA, thereby parallelizing the replication process. We show that anti-parallel strand orientation is essential for such a replicative organization of DNA, given our premises, the most important of which is the assumption of the presence of sequence-dependent asymmetric cooperativity in DNA.
Highlights
DNA in all living systems shares common properties that are remarkably well suited to its function, suggesting refinement by evolution
Within the picture we develop below, the evolutionary advantage of anti-parallel strand orientation of DNA arises from its ability to temporally parallelize the replication process, by dividing DNA into predictable, independent, simultaneously replicating segments, thereby speeding up the replication process considerably
We have argued that anti-parallel strand orientation of DNA enables independent unzipping and replication of multiple segments of DNA simultaneously, from predictable origins of replication, through sequence-dependent asymmetric cooperativity, since the stronger sequence-independent part is cancelled due to the anti-parallel orientation of the two strands of the duplex. Such a replicative organization would result in substantially shorter replication time for self-replicating heteropolymers with anti-parallel strands, when compared to heteropolymers with parallel strands
Summary
DNA in all living systems shares common properties that are remarkably well suited to its function, suggesting refinement by evolution. The evolutionary pressures that resulted in the adaptation of the specific physico-chemical properties of DNA are yet to be clearly elucidated, Such an evolution-based inquiry can be a useful alternative to the traditional biochemical approaches to unravel the functional significance of the structure and sequence of DNA. We identify an evolutionary advantage for the anti-parallel orientation of the two strands of the DNA duplex The importance of such an evolution-based explanation for anti-parallel strand orientation[5] stems from the fact that the latter is directly responsible for the biochemically cumbersome and complicated lagging strand replication mechanism of DNA, the existence of which militates against the well-established notion that DNA is a product of prebiotic evolutionary optimization. “Asymmetric Cooperativity”, a new property we introduced earlier and which we assume to be present in DNA, underpins the ability of anti-parallel strands to temporally parallelize DNA replication
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