Hi Walter, You should definitely detwin data for map calculation if you have a significant twinning fraction (and only for maps; keep using the twinned data set for refinement). We use the CCP4 program detwin. BUT if Shelxl gives bad density, maybe that's simply what you have, a bad density map - because output from Shelx is already detwinned! BTW, we observed that different programs handled different cases differently well; I would suggest ALWAYS to try more than one program, and also to try Phenix ... Best Clemens
-----Ursprüngliche Nachricht----- Von: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] Im Auftrag von Walter Kim Gesendet: Monday, March 16, 2009 7:22 AM An: CCP4BB@JISCMAIL.AC.UK Betreff: [ccp4bb] Twinned data and maps Hi again, Thanks for your insight into refinement tools for twinned data. I have a couple of twinned data sets that are nearly perfectly pseudomerohedrally twinned. I've begun to refine my data in Refmac5 (using the automated twin refinement), CNS (using the twin inputs) and Shelxl; I'm testing out the different refinement programs to evaluate the best strategy for the refinement. However, I would like to start making maps. 1. Refmac5 - outputs an mtz that is model-biased 2. CNS - maps made via model_map_twin.inp are poor 3. Shelxl - the maps generated in coot from the.fcf file are poor Are there better ways to make cleaner maps with my twinnned data that are less model-biased that I can try to build into? Should I detwin the data and make maps from that (but continue to refine against the twinned data)? Thanks, Walter
