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Premelting thermal fluctuational interbase hydrogen‐bond disrupted states of a B‐DNA guanine–cytosine base pair: Significance for amino and imino proton exchange

1991; Wiley; Volume: 31; Issue: 11 Linguagem: Inglês

10.1002/bip.360311105

1097-0282

Yu Chen, Wei Zhuang, E. W. Prohofsky,

Microfluidic and Capillary Electrophoresis Applications

Abstract 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(dG) · 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 inter base H bond. The imino proton exchange, however, requires the disruption of all three inter base 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.