Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)

This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands

Theoretical study of the tautomerism in the one-electron oxidized guanine-cytosine base pair

Ionizing radiation on DNA mainly generates one-electron oxidized guanine-cytosine base pair (G(+.):C), and in the present paper we study all possible tautomers of G(+.):C by using ab initio approaches. Our calculations reveal that the tautomeric equilibrium follows a peculiar path, characterized by a stepwise mechanism: first the proton in the central hydrogen bond N1(G)-H1-N3(C) migrates from guanine to cytosine, and then the cytosine cation releases one proton from its amino group. During this second step, water acts as a proton acceptor, localizing the positive charge on one of the water molecules interacting with the guanine radical. In agreement with experimental findings, the computed energy barriers show that the deprotonation of the cytosine cation is the speed-limiting step in the tautomeric equilibrium. The influence of the number of water molecules incorporated in the theoretical model is analyzed in detail. The evolution of electronic properties along the reaction path is also discussed on the basis of partial atomic charges and spin density distributions. This work demonstrates that water indeed plays a crucial role in the tautomeric equilibra of base pairs

Impact of DNA Environment on the Intrastrand Cross-Link Lesions: Hydrogen Atom Release as the Last Step of Formation of G[8-5m]T

International audienceOxidative intrastrand cross-links where two nucleobases are covalently tethered form a particularly harmful class of DNA lesions. Their formation follows a radical pathway, as initiated by reactive oxygen species, which often ends with the departure of the hydrogen H8 of guanine to restore a closed-shell adduct. The ease of this abstraction step is investigated here for three systems of increasing complexity, C8-methyleguanine, the guanine-thymine dinucleoside monophosphate (GpT), and GpT embedded in a hexameric DNA sequence. First-principle calculations, combined with semiempirical approaches for the latter system, are performed to determine the energetics of the intermediates and to compare their respective exergonicities, which turned out to significantly depend on the environment. The hydrogen departure path is shown to be strongly favored compared to usual H-abstraction sites for normal guanine, while the impact of the biological environment is evidenced as the H8 departure becomes more difficult when larger structures are considered. A computational assessment of a plausible oxime intermediate is discussed as well