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Semper: Distortion Compensation, Selective Averaging, 3-D Reconstruction, and Transfer Function Correction in a
1Department of Materials Science and Metallurgy, Pembroke Street, Cambridge, CB2 3QZ, United Kingdom1 1Most of the Semper tools specifically devised for macromolecular structure determination in 3D were developed during visits to the Max Planck Institute for Biochemistry, W-8033 Martinsried-bei-Munchen, Germany.
Abstract:
The Semper system was developed 20 years ago to address problems of 2-D image averaging and transfer function correction. User extendibility was an important design requirement, and a very considerable body of extensions have been written in the interim; this paper reviews those most relevant to macromolecular structure determination by 2-D and 3-D electron microscopy. The techniques best provided for are distortion-compensated averaging (correlation averaging and local unbending), selective averaging (of several kinds), 3-D reconstruction of 2-D crystals, and transfer function estimation and correction. The (normally interactive) control language is flexible enough to be a frequently preferred alternative to programming at any lower level.