Conformational properties of a UV-damaged DNA decamer containing a cis.syn cyclobutane thymine dimer (PD) have been investigated by molecular dynamics (MD) simulations. Results from MD simulations of the damaged decamer DNA show a kink of approximately 21.7 degrees at the PD damaged site and a disruption of H bonding between the 5'-thymine of the PD and its complementary adenine. However, no extra-helical flipping of the 3'-adenine complementary to the PD was observed. Comparison to two undamaged DNA decamers, one with the same sequence and the other with an AT replacing the TT sequence, indicates that these properties are specific to the damaged DNA. Essential dynamics (ED) derived from the MD trajectories of the three DNAs show that the backbone phosphate between the two adenines complementary to the PD of the damaged DNA has considerably larger mobility than the rest of the molecule and occurs only in the damaged DNA. As observed in the crystal structure of T4 endonuclease V in a complex with the damaged DNA, the interaction of the enzyme with the damaged DNA can lead to bending along the flexible joint and to induction of adenine flipping into an extra-helical position. Such motions may play an important role in damage recognition by repair enzymes.