ISSN:0741-0581    

DOI:10.1002/jemt.1060090402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractMethods are described for the analysis of electron micrographs of regular biological objects. Fourier‐based processing of one‐dimensionally ordered arrays is described by way of introduction, before analysing two‐dimensional crystals in projection with the aim of enhancing signal:noise ratio and thus of feint features that were initially obscured. This form of analysis is then extended to decomposing the moiré patterns formed when sheets overlap, thereby enabling the separation of interfering image patterns. Analogous forms of an analysis can also be applied to objects with rotational symmetry. Methods for treating the effect of the microscope imaging system and compensating for lattice disorder in crystalline specimens are also dis

ISSN:0741-0581    

DOI:10.1002/jemt.1060090403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractMethods are described for the analysis of electron micrographs of biological objects with helical symmetry and for the production of three‐dimensional models of these structures using computer image reconstruction methods. Fourier‐based processing of one‐ and two‐dimensionally ordered planar arrays is described by way of introduction, before analysing the special properties of helices and their transforms. Conceiving helical objects as a sum of helical waves (analogous to the sum of planar waves used to describe a planar crystal) is shown to facilitate analysis and enable three‐dimensional models to be produced, often from a single view of the object. The corresponding Fourier transform of such a sum of helical waves consists of a sum of Bessel function terms along layer lines. Special problems deriving from the overlapping along layer lines of terms of different Bessel order are discussed, and methods to separate these terms, based on analysing a number of different azimuthal views of the object by least squares, are described. Corrections to alleviate many technical and specimen‐related problems are discussed in conjunction with a consideration of the computer methods used to actually process an image. A range of examples of helical objects, including viruses, microtubules, flagella, actin, and myosin filaments, are discussed to illustrate the range of problems that can be addressed by computer reconstruct

ISSN:0741-0581    

DOI:10.1002/jemt.1060090404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractTo overcome the radiation damage‐induced limitations to the resolution of three‐dimensional reconstructions from electron microscopic tilt series, novel reconstruction schemes have been developed that require only a single exposure of the specimen. The tilt series collected with these methods have random projection directions. First, three‐dimensional reconstruction techniques are described that are applicable to data obtained from tilt series with regular tilt geometry, followed by the extensions of these techniques to permit analysis of projection series with randomly spaced tilts. The main emphasis is placed on the weighted back‐projection methods, which have recently been extended so as to be applicable to random tilt series. Besides a description of the algorithms, the complete procedure for a threedimensional reconstruction from a single‐exposure, random conical tilt series is explained, including the determination of the azimuthal angles, the alignment scheme for conical tilt series, the dependence of the achievable resolution on the number of projections for regular conical and single‐axis geometries, and the method to calculate the actual resolution of two‐dimensional image averages and of three‐dimensional reconstructions using the phase residual and Fourier ring correlation criteria. Examples are given of biological specimens to which these three‐dimensional reconstruction methods

ISSN:0741-0581    

DOI:10.1002/jemt.1060090405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractA comprehensive computer‐graphics‐based system (STERECON) is described for tracing and digitizing contours from individual or stereopair electron micrographs. The contours are drawn in parallel planes within the micrographs. Provision is also made for tracing and digitizing in full three‐dimensional (3‐D) coordinates in any direction along linear structures such as cytoskeletal elements. The stereopair micrographs are viewed in combination with the contours being traced on a graphics terminal monitor. This is done either by projecting original electron micrograph (EM) negatives onto a screen and optically combining these images with contour lines being drawn on the monitor, or by first digitizing the images and displaying them directly on the monitor along with the contour lines. Prior image digitization allows computer enhancement of the structures to be contoured. Correction and alignment routines are included to deal with variable section thickness, section distortion and mass loss, variations in photography in the electron microscope, and terminal screen curvature when combining projected images with contour lines on the monitor. The STERECON system organizes and displays the digitized data from successive sections as a 3‐D reconstruction. Reconstructions can be viewed in any orientation as contour stacks with hidden lines removed; as wire‐frame models; or as shaded, solid models with variable lighting, transparency, and reflectivity. Volumes and surface areas of the reconstructed objects can be determined. Particular attention was paid to making the system convenient for the biological user. Users are given a choice of three different stereo‐vi

ISSN:0741-0581    

DOI:10.1002/jemt.1060090406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

摘要:

AbstractThe surface protein of the archaebacteriumPyrodictium occultumforms two‐dimensional periodic arrays of extremely poor order. Two variants of correlation averaging have been applied in order to retrieve the unit cell structure from electron micrographs of negatively stained samples: straightforward correlation averaging correcting for lateral displacements only and a more elaborate approach, including a partial compensation for rotational disorder. Surprisingly, both routes yield virtually identical structures. Inclusion of molecular motifs from highly disordered domains, which are rejected in the “straightforward” approach, appears not to improve resolution, possibly because the high local strain tends to distort the individual mole

ISSN:0741-0581    

DOI:10.1002/jemt.1060090407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060090408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060090409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY

ISSN:0741-0581    

DOI:10.1002/jemt.1060090401

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1988

数据来源: WILEY