Um temporizador mutacional embutido na química do DNA: mero acaso, fortuita necessidade ou design inteligente?

quinta-feira, fevereiro 01, 2018

Dynamic basis for dG•dT misincorporation via tautomerization and ionization


Received:10 June 2016 Accepted:21 December 2017 Published online:31 January 2018

Source/Fonte: Instapge


Tautomeric and anionic Watson–Crick-like mismatches have important roles in replication and translation errors through mechanisms that are not fully understood. Here, using NMR relaxation dispersion, we resolve a sequence-dependent kinetic network connecting G•T/U wobbles with three distinct Watson–Crick mismatches: two rapidly exchanging tautomeric species (Genol•T/UG•Tenol/Uenol; population less than 0.4%) and one anionic species (G•T–/U–; population around 0.001% at neutral pH). The sequence-dependent tautomerization or ionization step was inserted into a minimal kinetic mechanism for correct incorporation during replication after the initial binding of the nucleotide, leading to accurate predictions of the probability of dG•dT misincorporation across different polymerases and pH conditions and for a chemically modified nucleotide, and providing mechanisms for sequence-dependent misincorporation. Our results indicate that the energetic penalty for tautomerization and/or ionization accounts for an approximately 10−2 to 10−3-fold discrimination against misincorporation, which proceeds primarily via tautomeric dGenol•dT and dG•dTenol, with contributions from anionic dG•dT– dominant at pH 8.4 and above or for some mutagenic nucleotides.

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