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MIR Tutorial Bath - Strategy

1. Strategy

Briefly, once the native and derivative datasets have been collected and processed, the solution of protein structures by the method of multiple isomorphous replacement (MIR), optionally with anomalous scattering (MIRAS), involves the following steps:

  1. Scaling each derivative dataset to the native.

  2. Either calculation of the isomorphous difference Pattersons, and location of the heavy-atom sites by vector search methods; or location of the heavy-atom sites by direct methods.

  3. Refinement of the heavy-atom parameters.

  4. Calculation of protein phases.

  5. Calculation of difference Fouriers to locate and check other sites, and if necessary to solve additional derivatives.

  6. Final calculation of phases and the electron-density map.

For a comprehensive exposition of the methods, consult the 1991 Proceedings of the CCP4 Study Weekend on "Isomorphous Replacement and Anomalous Scattering". Most of the examples to be shown here illustrate the use of programs distributed in the CCP4 package, though several other packages are available that contain very similar programs.