Ab initio HF crystal orbital calculations were performed for a guanine-cytosine base pair stack at its equilibrium position and at 0.05 angstrom dilatation and compression, respectively. The shifts of the conduction and valence band edges were used to determine the deformation potentials of the electrons and the holes. After performing an approximate calculation for the elastic constant, the mobilities of the electrons and holes were determined. They were combined with the mobilities belonging to the longitudinal and torsional motions at a stack in DNA. (c) 2006 Elsevier B.V. All rights reserved.