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Cover illustration: Porcine pancreatic elastase, [100] section of the model envelope m(x) (p. 1316). 
Acta Cryst. (2000). D56, 12051214 [ doi:10.1107/S0907444900009355 ] Direct methods and protein crystallography at low resolutionC. J. GilmoreSynopsis: This paper discusses how the phase problem in protein crystallography needs atomic resolution data for ab initio modelfree phasing to work. Online October 2000 
Acta Cryst. (2000). D56, 12151222 [ doi:10.1107/S0907444900010787 ] Macromolecular structure determination by cryoelectron microscopyH. R. SaibilSynopsis: This paper reviews the contribution and future potential of cryoelectron microscopy and threedimensional reconstruction in the determination of macromolecular structures. Online October 2000 
Acta Cryst. (2000). D56, 12231232 [ doi:10.1107/S0907444900010088 ] Lowresolution ab initio phasing: problems and advancesV. Y. Lunin, N. L. Lunina, T. E. Petrova, T. P. Skovoroda, A. G. Urzhumtsev and A. D. PodjarnySynopsis: A lowresolution phasing statistical approach is presented and figures of merit which may be used successfully for phasing are discussed. Online October 2000 
Acta Cryst. (2000). D56, 12331244 [ doi:10.1107/S0907444900009331 ] Density constraints and lowresolution phasingA. G. Urzhumtsev, N. L. Lunina, T. P. Skovoroda, A. D. Podjarny and V. Y. LuninSynopsis: Applications of different density constraints in lowresolution phasing are discussed. Online October 2000 
Acta Cryst. (2000). D56, 12451252 [ doi:10.1107/S0907444900009343 ] Ab initio lowresolution phasing in crystallography of macromolecules by maximization of likelihoodT. E. Petrova, V. Y. Lunin and A. D. PodjarnySynopsis: The possibility of using the statistical likelihood as a figure of merit in lowresolution ab initio phasing is tested. Online October 2000 
Acta Cryst. (2000). D56, 12531258 [ doi:10.1107/S090744490001115X ] Structural analysis of noncrystalline macromolecules: the ribosomeE. V. OrlovaSynopsis: A description of the main steps of the structural analysis of noncrystalline biological macromolecules using cryoelectron microscopy is given in this paper. Online October 2000 
Acta Cryst. (2000). D56, 12591269 [ doi:10.1107/S0907444900011252 ] Assessment of electron crystallographic data obtained from twodimensional crystals of biological specimensV. M. UngerSynopsis: Electron crystallographic data from 2D crystals are being generated and published at an accelerating pace. However, unlike in Xray crystallography, there are no standardized criteria in electron crystallography that can help investigators and reviewers alike to judge the reliability of electron crystallographic data. This article discusses some of the relevant issues and intends to serve as a platform for further discussion. Online October 2000 
Acta Cryst. (2000). D56, 12701277 [ doi:10.1107/S0907444900009549 ] Resolution measurement in structures derived from single particlesN. GrigorieffSynopsis: Analytical expressions are derived and computer simulations are used to assess the accuracy of common resolution measures for protein structures derived from images of single molecules of complexes. It is concluded that the alignment of images is accompanied by a correlation of noise, and that this correlation leads to erroneous resolution measurements. Online October 2000 
Acta Cryst. (2000). D56, 12781287 [ doi:10.1107/S0907444900010817 ] Supplanting crystallography or supplementing microscopy? A combined approach to the study of an enveloped virusE. J. Mancini and S. D. FullerSynopsis: The complementarity of Xray and cryoelectron microscopy results is illustrated in the determination and interpretation of the structure of an enveloped virus at 9 Å resolution. Online October 2000 
Acta Cryst. (2000). D56, 12881303 [ doi:10.1107/S0907444900009574 ] Lowresolution phase information in multiplewavelength anomalous solvent contrast variation experimentsW. Shepard, R. Kahn, M. Ramin and R. FourmeSynopsis: A complete account of the MASC method is given from the basic theory and experimental considerations through to the phasing of the macromolecular envelope at low resolution. Online October 2000 
Acta Cryst. (2000). D56, 13041311 [ doi:10.1107/S0907444900008982 ] Inhouse lowresolution Xray crystallographyG. Evans, P. Roversi and G. BricogneSynopsis: Modifications to a standard inhouse Xray diffraction camera (ElliotGX13/300 mm MAR IP) are presented which allow the measurement of very low resolution diffraction intensities (>200 Å). Online October 2000 
Acta Cryst. (2000). D56, 13121315 [ doi:10.1107/S0907444900008970 ] The oversampling phasing methodJ. Miao, J. Kirz and D. SayreSynopsis: Sampling the diffraction pattern of a finite specimen more finely than the Nyquist frequency corresponds to surrounding the electron density of the specimen with a nodensity region. This nodensity region can be used to retrieve the phase information directly from the diffraction pattern. Online October 2000 
Acta Cryst. (2000). D56, 13161323 [ doi:10.1107/S0907444900008490 ] Modelling prior distributions of atoms for macromolecular refinement and completionP. Roversi, E. Blanc, C. Vonrhein, G. Evans and G. BricogneSynopsis: Homographic exponential models give a compact representation of probability distributions for the missing part of a macromolecular crystal structure and for the bulk solvent. These distributions are used in the maximumlikelihood refinement and maximumentropy completion of partial structures. PDB reference: 1lvy Online October 2000 
Acta Cryst. (2000). D56, 13241331 [ doi:10.1107/S0907444900010283 ] Lowresolution phase extension using wavelet analysisP. Main and J. WilsonSynopsis: Predicted values for wavelet coefficients are used to extend phases from 10 Å to around 67 Å. Online October 2000 
Acta Cryst. (2000). D56, 13321340 [ doi:10.1107/S0907444900010908 ] Docking structures of domains into maps from cryoelectron microscopy using local correlationA. M. RosemanSynopsis: Atomic models of large macromolecular complexes can be built by docking the atomic structures of components into cryoEM maps. A procedure based on local realspace correlation is presented and verified by docking the domains from the crystal structure of GroEL into a cryoEM map of the oligomer. Online October 2000 
Acta Cryst. (2000). D56, 13411349 [ doi:10.1107/S0907444900009562 ] Fitting atomic models into electronmicroscopy mapsM. G. RossmannSynopsis: Techniques are described and examples are given for the interpretation of lower resolution cryoEM results by using higher, near atomic resolution crystallographic results of component structures. Online October 2000 
Acta Cryst. (2000). D56, 13501357 [ doi:10.1107/S0907444900009410 ] When two into one won't go: fitting in the presence of steric hindrance and partial occupancyE. Thouvenin and E. HewatSynopsis: Two techniques of fitting Xray to EM data in the presence of steric hindrance are presented and applied to a rotavirusFab complex. As the Xray structures of the Fab and the Fab bound to a viral protein are known, this is a good test case. Online October 2000 
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