DNA STRAND SEPARATION STUDIED BY SINGLE-MOLECULE FORCE MEASUREMENTS

We have separately attached the two complementary strands of one end o f a DNA double helix to a glass slide and a glass microneedle. Displac ing the slide away from the needle, the molecule is progressively pull ed open and the changing deflection of the needle gives the correspond ing variation in the opening force. Force signals which are very rich in detail are reproducibly obtained. The average level and amplitude o f the force signal is almost independent of the opening velocity in th e interval 20 nm/s to 800 nm/s. A theoretical description based on the assumption of thermal equilibrium allows us to link the measured forc e curves to the genomic sequence of the DNA. A molecular stick-slip mo tion is revealed, which in contrast to the dynamics of macroscopic sol id friction is a deterministic and reproducible process. This process is considered experimentally theoretically.