Tables for
Volume B
Reciprocal space
Edited by U. Shmueli

International Tables for Crystallography (2006). Vol. B. ch. 2.3, p. 261


M. G. Rossmanna* and E. Arnoldb

aDepartment of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA, and  bCABM & Rutgers University, 679 Hoes Lane, Piscataway, New Jersey 08854-5638, USA
Correspondence e-mail:

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Molecular replacement: phase refinement as an iterative process

(A)[{\bf F}_{\rm obs}, \alpha'_{n}, m'_{n} \rightarrow \rho_{n}]
(B) [\rho_{n} \rightarrow \rho_{n}](modified)
  (i) Use of noncrystallographic symmetry operators
  (ii) Definition of envelope limiting volume within which noncrystallographic symmetry is valid
  (iii) Adjustment of solvent density
  (iv) Use of crystallographic operators to reconstruct modified density into a complete cell
(C) [\rho_{n} \hbox{(modified)} \rightarrow {\bf F}_{{\rm calc}, \,  n + 1}\hbox{; } \alpha_{{\rm calc}, \,  n + 1}]
(D) [({\bf F}_{{\rm calc}, \,  n + 1}, \alpha_{{\rm calc}, \,  n + 1}) + ({\bf F}_{\rm obs}, \alpha_{0}) \rightarrow {\bf F}_{\rm obs}, \alpha'_{n + 1}, m'_{n + 1}]
  (i) Assessment of reliability of new phasing set [\alpha_{n + 1}] in relation to original phasing set [\alpha_{0}(w)]
  (ii) Use of figures of merit [m_{0}, m_{n + 1}] and reliability w to determine modified phasing set [\alpha'_{n + 1}, m'_{n + 1}]
  (iii) Consideration of [\alpha_{n + 1}] and [m_{n + 1}] where there was no prior knowledge of
   (a) [{\bf F}_{\rm obs}] (e.g. very low order reflections or uncollected data)
   (b) [\alpha_{0}] (e.g. no isomorphous information or phase extension)
(E) Return to step (A) with [\alpha'_{n + 1}, m'_{n + 1}] and a possibly augmented set of [{\bf F}_{\rm obs}].
Wang (1985)[link]; Bhat & Blow (1982)[link]; Collins (1975)[link]; Schevitz et al. (1981)[link]; Hoppe & Gassmann (1968)[link].
Rossmann & Blow (1961)[link]; Hendrickson & Lattman (1970)[link].