Dear All, I have 1.4 A data and a molecular replacement solution for a crystal indexed as C2, with beta approximately equal to 90. Refinement with refmac is progressing poorly, and intensity statistics (Truncate) and other twinning tests (xtriage) suggest pseudo-merohedral twinning with a twin fraction around 0.44. I want to try refining in SHELXL with a twin-specific target function, but I have some questions about how to get started.
SHELX documentation indicates that the reflection file should contain intensities rather than amplitudes, and preferably unmerged data. I have been refining against an mtz file that was integrated with MOSFLM, scaled and merged with SCALA, converted to amplitudes with TRUNCATE, then had freeR flags assigned. I am getting the mtz2various patch recently mentioned on the bb, that will make an mtz file into a proper SHELX hkl file, but which mtz file do I convert? The mtz output by TRUNCATE contains both F's and I's, so I could use that one to get measured intensities, or do I actually need to go back further to get my unmerged reflections? A second question relates to Rfree flags - should I transfer the ones I've been using up until now? They were a randomly assigned 5%. Now I've read that using the "thin shell" method is better for twinned crystals and NCS, but I don't know exactly how that is done... any recommendations? Thanks! Evette Evette S. Radisky, Ph.D. Assistant Professor and Associate Consultant II Mayo Clinic Cancer Center Griffin Cancer Research Building, Rm 310 4500 San Pablo Road Jacksonville, FL 32224 (904) 953-6372 (office) (904) 953-2857 (lab)
