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Low-resolution phase extension and refinement by maximum entropy

Abstract : The problem of phase refinement and extension at very low resolution (30-25 ~) is treated with an algorithm that combines a maximum-entropy approach, a binary modelling of the electron density, refinement of the proposed map against the observed amplitudes and solvent flattening outside a molecular envelope. The algorithm is applied to data for the complex of aspartyl-tRNA and aspartyl-tRNA syn- thetase in three different cases: (1) X-ray amplitudes and phases calculated from a partial model; (2) mixed observed and calculated X-ray amplitudes and phases from a partial model; and (3) observed neutron amplitudes and phases from a very approximate model. The change of correlation with the correct map at 30 A resolution is used as a measure of correctness. Upon application of the algorithm, this correlation changes from 59 to 97% in case 1, from 59 to 77% in case 2 and from 72 to 90% in case 3. In all cases, the method is successful in correcting large phase errors, deleting noise regions and producing the correct low-resolution molecular image.
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Submitted on : Tuesday, February 9, 2021 - 4:54:49 PM
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A. Podjarny, D. Moras, J. Navaza, P. Alzari. Low-resolution phase extension and refinement by maximum entropy. Acta Crystallographica Section a Foundations of Crystallography, Wiley-Blackwell, 1988, 44 (4), pp.545-551. ⟨10.1107/S0108767388002971⟩. ⟨pasteur-03136422⟩



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