Cover Picture

Arnaud David, Nathalie Bleimling, Christine Beuck, Jean-Marie Lehn, Elmar Weinhold, and Marie-Paule Teulade-Fichou

The cover picture shows how the conformational equilibrium of a nucleobase in DNA canbe changed from the predominant intrahelical position to the extrahelical position(center). This process of base (nucleotide) flipping is achieved naturally by DNAglycosylases and DNA methyltransferases like M.TaqI, which binds the target base in itsextrahelical conformation and fills the resulting hole in the DNA (left). Base flipping canalso be induced by a small synthetic bisacridine macrocycle that specifically inserts atthermodynamically weakened sites (e.g. base mismatches) in DNA and hence stabilizes theextrahelical conformation of a nucleobase (right). Further details on binding of thebisacridine macrocycle to DNA can be found in the article byE. Weinhold, M.-P. Teulade-Fichou et al. on p. 1326 ff.