Premelting thermal fluctuational interbase hydrogen-bond disrupted states of a B-DNA guanine–cytosine base pair: Significance for amino and imino proton exchange
✍ Scribed by Y. Z. Chen; W. Zhuang; E. W. Prohofsky
- Publisher
- Wiley (John Wiley & Sons)
- Year
- 1991
- Tongue
- English
- Weight
- 829 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0006-3525
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✦ Synopsis
Modified self-consistent phonon theory when applied to the DNA double helix indicates the existence of fairly long-lived states in which single interbase H bonds are disrupted. One can then postulate a number of situations in which particular disrupted H bonds can enhance particular proton exchange. In this paper we postulate a number of such partially open states for a B-conformation GC base pair and calculate the probability of each of these states for a B-conformation poly ( d G )poly (dC) . We compare these probabilities to those probabilities needed to explain various observed proton exchange rates. We propose that, for a GC base pair in B conformation, there are two amino proton exchangeable states-a cytosine amino proton exchangeable state and a guanine amino proton exchangeable state; both require the disruption of only the corresponding interbase H bond. The imino proton exchange, however, requires the disruption of all three interbase H bonds and this defines a third open state. Our calculated probabilities for a GC base pair in these three states are in fair agreement with available experimental estimates from measurements of amino and imino proton exchange.