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
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