Showing papers by "Carlos Bustamante published in 1990"
TL;DR: The dynamics of individual DNA molecules undergoing orthogonal field alternating gel electrophoresis (OFAGE) have been studied by use of T2 DNA molecules labeled with a dye and visualized with a fluorescence microscope and a classification of various reorientation mechanisms observed in molecules that form kinks is presented.
Abstract: The dynamics of individual DNA molecules undergoing orthogonal field alternating gel electrophoresis (OFAGE) have been studied by use of T2 DNA molecules labeled with a dye and visualized with a fluorescence microscope. The mechanism of reorientation used by a molecule to align itself in the direction of the new orthogonal field depends on the degree of extension of the chain immediately before the application of this field. The formation of kinks is promoted when time is allowed between the application of the two orthogonal fields so that the molecule attains a partially relaxed configuration. In this case, the chain appears bunched up in domains moving along the contour of the molecule. These regions are found to be the locations where the kinks are formed upon application of the second field perpendicular to the chain. The formation of kinks provides a significative retardation of the reorientation of the molecules, relative to molecules that do not form kinks, and appears to play an important role in the fractionation attained with ORAGE. A classification of various reorientation mechanisms observed in molecules that form kinks is presented.
106 citations
TL;DR: In this paper, the authors used tunneling microscopy to obtain high-resolution images of biological molecules under conditions that resemble those in vivo, and they used this approach to image intact T7 and fd bacteriophages and lysed T7 phages.
Abstract: One of the primary goals of scanning tunneling microscopy (STM) work in biology is to obtain high‐resolution images of biological molecules under conditions that resemble those in vivo. To accomplish this goal two main difficulties need to be overcome. (1) Problems caused by the low conductivity of biological material, and (2) depositing the sample in a controlled and reliable way on a flat, inert conducting substrate. The first problem can be solved by coating the sample with a thin metal layer, at some cost in resolution. This allows the second problem, controllable depositing the sample, to be approached systematically, independent of difficulties caused by low conductivity. Using this approach, two different kinds of viruses have been imaged, bacteriophage T7 and fd. STM images of intact T7 and fd bacteriophages, and lysed T7 phages have been obtained in a straightforward and routine way. To obtain high‐resolution images it is necessary to use uncoated samples. The conductivity problems cannot be avoided in this case, but they can be minimized by using thin samples. We have been able to obtain STM images of uncoated DNA molecules with about 10 A resolution, in a variety of packing arrangements and conformations. One conclusion resulting from these experiments is that the STM tip often makes contact with uncoated molecules and sweeps them aside rather than imaging them. The mechanism of conduction through the DNA, and methods by which the tip contact problem can be overcome are discussed.
22 citations
TL;DR: The dynamics of single DNA molecules undergoing steady-state and pulsed-field gel electrophoresis have been studied using T2 DNA molecules labeled with acridine orange and visualized with a fluorescence microscope, and it was observed that DNA molecules moving through the gel display an extension-contraction motion.
15 citations
TL;DR: In this paper, the electro-optic properties of sputterdeposited PLZT, BaTiO 3, SBN, and BNN films on fused silica substrates have been studied using a confocal scanning optical polarization microscope.
Abstract: The electro-optic properties of sputter-deposited PLZT, BaTiO 3 , SBN, and BNN films on fused silica substrates have been studied using a confocal scanning optical polarization microscope. The Pockels, Kerr, and higher order electro-optic coefficients and their relations to the non-linear optical coefficients in the films are presented. The materials and physical properties of the films are discussed.
14 citations
TL;DR: Observations identify several mechanisms of condensation available to higher order structures of DNA, and indicate that kinks are an important intermediate step in many of the transitions.
Abstract: The fluorescent dye, acridine orange, was used to visualize bacterial chromosomes extending from bacteria attached to a glass surface. The acridine-induced condensation of these chromosomes was followed in real-time with a low light level video camera. Acridine orange induced the packing of the bacterial chromosome into thick bundles which underwent various forms of condensation, supercoiling, folding, and rolling into a compact particle. Filaments attached to the surface at both ends were topologically constrained and supercoiled rapidly; whereas all three patterns of condensation were noted among filaments attached at only one end or free from the surface. Kinks often appeared in the filaments prior to supercoiling or folding, and the dynamic events observed often occurred around these kinks. These observations identify several mechanisms of condensation available to higher order structures of DNA, and indicate that kinks are an important intermediate step in many of the transitions.
9 citations
06 Jun 1990
TL;DR: In this article, the results of electrooptic and nonlinear optical (NLO) studies in several thin-film materials deposited on fused silica substrates have been reported, and the potential applications of these films are discussed.
Abstract: The authors report the results of electrooptic (EO) and nonlinear optical (NLO) studies in several thin-film materials deposited on fused silica substrates. Using a transparent substrate allowed observation of the EO and NLO effects easily by using optical-transmission-type measurements. PLZT, BaTiO/sub 3/, SBN, BNN, and beta-BBO thin-film materials were studied. The material properties and the potential applications of these films are discussed. >
1 citations
06 Jun 1990
TL;DR: In this paper, the authors describe the deposition of PLZT films and the design and testing of two-dimensional electrooptic modulators using these films, and several material and device related problems are addressed.
Abstract: The authors describe the deposition of PLZT films and the design and testing of two-dimensional electrooptic modulators using these films. Several material and device related problems are addressed. It has been demonstrated that PLZT films show strong electrooptic, pyroelectric, piezoelectric, photorefractive, and nonlinear optical effects, and some prototype devices have been made. >
1 citations
01 Aug 1990
TL;DR: It is found that the mechanism of formation of hooks require the previous generation of a kink (in which parts of the molecule double up inside a pore) in the size-dependent separation observed in PFGE experiments.
Abstract: The mechanisms of reorientation of individual DNA molecules undergoing Pulsed Field Gel Electrophoresis (PFGE) have been studied using T2 DNA molecules labeled with acridine orange and visualized with a fluorescence microscope. It is shown that molecules undergoing PFGE and conventional electrophoresis often get trapped in hook conformations (narrow U-shapes) that play an important role in determining the mobility of the molecules. It is found that the mechanism of formation of hooks require the previous generation of a kink (in which parts of the molecule double up inside a pore). Computer simulation experiments are presented to clarify the role of hook and kink formation in the size-dependent separation observed in PFGE experiments.
TL;DR: The superposition principle states that the angledependent difference in scattering intensities for right and left circularly polarized light, for chiral structures composed of various hierarchical levels, is the sum of the contributions from each level taken separately.
Abstract: The superposition principle states that the angle‐dependent difference in scattering intensities for right and left circularly polarized light, for chiral structures composed of various hierarchical levels, is the sum of the contributions from each level taken separately. Analytic expressions describing this superposition are obtained for oriented and rotationally averaged hierarchical chiral structures. It is shown that the superposition principle holds only when the coiling levels in the chiral structure are disparate. In particular, for a structure composed of two chiral levels, the lower order structure must be much smaller than both the wavelength of light and the higher order structure. Numerical calculations using these expressions are carried out for superhelices of varying dimensions.