Dear all,
Twin refinement has yielded Rwork/Rfree values of about 0.10/0.12 for a nice quality 1.8A dataset (Rmerge 6%, space group I4, twin fractions 0.6/04) and almost the same R/Rfree (0.095/0.115) for another 1.5A nice quality data set (Rmerge 6%, space group I4, twin fractions 0.74/0.26). Refinement of untwinned data resulted in Rfree of ~32% and ~22% respectively. REFMAC and PHENIX both have produced the same results and almost identical R factors, which are suspiciously VERY LOW for this resolution of data. Twin refinement in REFMAC has produced exceptional quality maps even for 1.8A data (they look rather like 1.2A maps) - I can not tell the same for PHENIX - maps were looking worse (may be someone has a better idea why). Normally twin refinement results in lowering R-factors - say, the drop in R from 30% (without twin refinement) to 20% (with twin refinement) would be considered normal, however we can see the drop from 32% to 12%. I wonder if anyone else has experienced similar problems and what would be the most reasonable explanation for that.
Thank you Yury Yury Patskovsky, Ph.D. Associate, Dept of Biochemistry Albert Einstein College of Medicine 1300 Morris Park Ave Bronx, NY 10461 phone 718-430-2745 yu...@medusa.vioc.aecom.yu.edu
