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DNA heteroduplexes containing base mismatches were studied for enhanced alkylation by altromycin B to identify the structural and/or dynamics behind enhanced drug reactivity. The results indicate that pluramycin reactivities are determined by the dynamic conformation of the base mismatch as well as by the specific groove interactions between the drug and the DNA. It is determined that the highest pluramycin reactivity with heteroduplex DNA is the result of a thymine:thymine mismatch.

Bezelesin is a DNA-DNA interstrand cross-linking agent that can translocate from a monoalkylation site to a thermodynamically favored cross-linking site. The thermodynamic stability of Bizelesin-cross-linked species coupled with the facile reversibility of the monoalkylated species gave rise to the accumulation of the cross-linked species. Furthermore, the amount of monoalkylation species decreased compared to the cross-linked species due to the fast alkylation of the cross-linking site.

The mechanism of covalent modification of DNA and the mode of interaction of sporospermin with DNA were determined. The results of high-field NMR and gel electrophoresis showed that intercalation of the DNA molecule by psorospermin, resulting in the site-directed electrophilic addition of the epoxide to N7 of guanine located to the '3 side of the site of DNA intercalation. The interaction was found to resemble that of the quinacrine nitrogen mustard and that of the mutagen, sterigmatocystin.

We study quantum corrections in four-dimensional theories with N = 1 supersymmetry in the context of Quantum Gravity Conjectures. According to the Emergent String Conjecture, infinite distance limits in quantum gravity either lead to decompactification of the theory or result in a weakly coupled string theory. We verify this conjecture in the framework of N = 1 supersymmetric F-theory compactifications to four dimensions including perturbative α′ as well as non-perturbative corrections. After proving uniqueness of the emergent critical string at the classical level, we show that quantum corrections obstruct precisely those limits in which the scale of the emergent critical string would lie parametrically below the Kaluza-Klein scale. Limits in which the tension of the asymptotically tensionless string sits at the Kaluza-Klein scale, by contrast, are not obstructed. In the second part of the paper we study the effect of quantum corrections for the Weak Gravity Conjecture away from the strict weak coupling limit. We propose that gauge threshold corrections and mass renormalisation effects modify the super-extremality bound in four dimensions. For the infinite distance limits in F-theory the classical super-extremality bound is generically satisfied by a sublattice of states in the tower of excitations of an emergent heterotic string. By matching the F-theory α′-corrections to gauge threshold corrections of the dual heterotic theory we predict how the masses of this tower must be renormalised in order for the Weak Gravity Conjecture to hold at the quantum level. [ABSTRACT FROM AUTHOR]

We investigate the interplay between the enumerative geometry of Calabi-Yau fourfolds with fluxes and the modularity of elliptic genera in four-dimensional string theories. We argue that certain contributions to the elliptic genus are given by derivatives of modular or quasi-modular forms, which may encode BPS invariants of Calabi-Yau or non-Calabi-Yau threefolds that are embedded in the given fourfold. As a result, the elliptic genus is only a quasi-Jacobi form, rather than a modular or quasi-modular one in the usual sense. This manifests itself as a holomorphic anomaly of the spectral flow symmetry, and in an elliptic holomorphic anomaly equation that maps between different flux sectors. We support our general considerations by a detailed study of examples, including non-critical strings in four dimensions. For the critical heterotic string, we explain how anomaly cancellation is restored due to the properties of the derivative sector. Essentially, while the modular sector of the elliptic genus takes care of anomaly cancellation involving the universal B-field, the quasi-Jacobi one accounts for additional B-fields that can be present. Thus once again, diverse mathematical ingredients, namely here the algebraic geometry of fourfolds, relative Gromow-Witten theory pertaining to flux backgrounds, and the modular properties of (quasi-)Jacobi forms, conspire in an intriguing manner precisely as required by stringy consistency. [ABSTRACT FROM AUTHOR]