CONFORMATIONAL TRANSITION OF LARGE DUPLEX T4 DNA EMBEDDED IN POLY(ACRYLAMIDE) GEL

Changes in the conformation of duplex T4 DNAs embedded in poly(acrylam ide) (PAAm) gels (as opposed to in an aqueous environment) were studie d using fluorescence microscopy for the observation of individual mole cules. In aqueous solutions, individual DNA chains exhibited thermal f luctuation, i.e., intramolecular and translational Brownian motion. Wi th the addition of acetone, DNAs were adsorbed onto the surface of a g lass plate accompanied by a discrete change in conformation from an el ongated coil into a collapsed globule, while ''metastable'' coiled DNA s were present in the buffer solution with a lifetime of several days. In contrast, in the gel phase, embedded DNAs did not exhibit thermal motion. With the addition of acetone, elongated-coil DNA underwent a s harp but continuous transition driven by the collapsing transition of the gel. The resulting compact DNA was shrunk less than the collapsed DNA in free aqueous solution. In addition, it is shown that elongation of the PAAm gel affects the orientation of the DNA chains.