Conformational transition in DNA on a cold surface

The contour length of DNA fragments, deposited and imaged on mica under buf fer, was measured as a function of deposition temperature. Extended DNA mol ecules (on Ni- and silane-treated surfaces) contract rapidly with falling t emperature, approaching the contour length of A-DNA at 2 degrees C. The con traction is not unique to a specific sequence and does not occur in solutio n at 2 degrees C or on a surface at 25 degrees C, indicating that it arises from a combination of low temperature and surface contact. It is probably a consequence of reduced water activity at a cold surface.