Information Runs The Show — The Understatement of the Century!
An interesting paper published in Nature by Evgenia et al. documents the ability of the DNA double helix to exist in a functional alternative form for 1% of the time, called an “excited state.” What does this mean for neo-Darwinism?
What is particularly remarkable is that the base-pairs present in these alternative forms show the ability to break apart and come together again to form stable structures which are non-characteristic of Watson-Crick base-pairing (called “Hoogsteen base pairs”). While these Hoogsteen base pairs have been observed before in instances where DNA has been subjected to damage or bound to drugs, this is the first time where such Hoogsteen base pairs have been observed under normal circumstances.
The authors report in the paper’s abstract,
Sequence-directed variations in the canonical DNA double helix structure that retain Watson-Crick base-pairing have important roles in DNA recognition, topology and nucleosome positioning. By using nuclear magnetic resonance relaxation dispersion spectroscopy in concert with steered molecular dynamics simulations, we have observed transient sequence-specific excursions away from Watson-Crick base-pairing at CA and TA steps inside canonical duplex DNA towards low-populated and short-lived A•T and G•C Hoogsteen base pairs. The observation of Hoogsteen base pairs in DNA duplexes specifically bound to transcription factors and in damaged DNA sites implies that the DNA double helix intrinsically codes for excited state Hoogsteen base pairs as a means of expanding its structural complexity beyond that which can be achieved based on Watson-Crick base-pairing. The methods presented here provide a new route for characterizing transient low-populated nucleic acid structures, which we predict will be abundant in the genome and constitute a second transient layer of the genetic code. [Emphasis mine]
The researchers used NMR to study the structure of the alternative form, and they concluded that the observed chemical shifts were characteristic of a structural orientation in which particular base-pairs are flipped 180 degrees to form a “Hoogsteen base pair.” This was further corroborated by computer modelling.
As the papers’ authors suggest, those results may imply that the DNA molecule is responsible for coding for excited state Hoogsteen base pairs as a means by which it can expand its structural complexity beyond that which it is able to achieve through classical Watson-Crick base-pairing.
If this prediction is correct, then it succeeds in adding a whole additional layer to the information enigma. This, of course, raises the pertinent issue of whether this discovery sits more comfortably with a neo-Darwinian paradigm or with an ID paradigm. Since neo-Darwinism, to date, may be considered to be demonstrably impotent to account for that specific property of living systems — namely, information — I would be inclined to significantly favour the latter.