Fractal‐like patterns in DNA films, B form at 0% relative humidity, and antiheteronomous DNA: An ir study

This report details the observation of (a) the intact double helix of DNA at 0% relative humidity in poly(dA) · poly(dT) and poly (dA‐dT) · poly (dA‐dT) films, (b) the fractal‐like growth of DNA crystals in films of poly (dA) · poly(dT), and (c) poly(dA) · poly(dT) with adenines in the B form and thymines in the A form. Observation (a) is based on the behavior of the middle ir signature of double‐helical base stacking, the 1714 cm −1 peak, at low water activity. This observation is modeled as a trapping of water in the polycrystalline part of these films. We interpret the glycosidic region of the middle ir spectra of the polycrystalline films of poly (dA) · poly (dT) at 0% relative humidity to indicate that at least part of the adenine strand in is the B conformation and the thymine strand is in the A form, whereas previous assignments of poly (dA) · poly (dT) films at 75% relative humidity indicated the opposite strand conformation assignment [E. Taillandier et al. (1987) Biochemistry , Vol. 26 p. 3361]. © 1994 John Wiley & Sons, Inc.