Interactions between metals and biomacromolecules including proteins, polysaccharides, and nucleic acids are important since they can be essential for a number of natural and industrial phenomena. These range from interactions of highly specific metal cofactors with particular proteins [1] to biosorption of heavy metals by polysaccharide hydrogels.[2]The unique features of DNA have been exploited in the development of novel materials, especially in the areas of medicine and nanotechnology. Classical research concerning antitumor drugs has focussed on the interactions of platinumor ruthenium-containing compounds with the major or minor grooves of polynucleotides. [3][4][5][6] There is a tremendous interest in the use of DNA in nanotechnology as a positioning template for the immobilization of metal nanoclusters with view to future applications in the construction of nanoelectronic devices. [7][8][9][10][11] Herein we report the interaction of Au 55 nanoclusters with the major grooves of B-DNA. The Au 55 clusters are degraded to Au 13 clusters by the transition of B-DNA into A-DNA in ultrahigh vacuum, and the resulting shrinkage of the major grooves. We have performed molecular-dynamics simulations and provided further information on the mechanism by which wires of Au 13 clusters form, and attempt to explain the interwire separation of 0.5 nm.