Introduction, Pre-crystallization modification, Crystallization, Post-crystallization treatment, Derivatization, Diffraction, Symmetry, Structure Solution, Structure Refinement, Structure Analysis & Presentation.

TOPIC DISCUSSION - Test Set and R-free

Editor: Please share your practice and theory on Test Set and R-free with fellow members of the group. A list of suggested subtopics is shown below. 

(1) How many reflections do you put in Test Set for R-free calculations, a centerin percentage or a certain number?

(2) For isomorphous structures, such as a wild type and several mutant structures crystallized in the same lattice, do you use the same Test Set for all these structures?

(3) Do you use the same Test Set if you re-process your data during refinement or obtain a better data set?

(4) Do you use the same Test Set when you switch refinement programs?

(5) What do you do to the Test Set if you find out the crystal is twinned during refinement without twinning considerations?

(6) Do you include some or all data in the Test Set for the final rounds of refinement?

      
Mark Mayer: How about an addition?

(7) When you have NCS do you pick Test Set using thin shells?

Recommended Reading: CCP4 wiki: R-factors

Twinning, Low Resolution Crystallography, PHASER, HKL2000, Parallel Protein Expression, Structural Genomics, NCS, Missing Atoms, Trends in Crystallography,  Absorption Correction.

Part 1: "How to read international tables?"

Part 2: "Data collection strategy" and "Twinning"

           "Phasing methods - a general introduction to all methods"

Part 3: "SAD phasing, Quick halide soaking, and Radiation damage 

           with possible use of it for phasing"