I experienced the same behavior. Crystals from the same drop could have varying twin fractions. Screening for twinning can be done with remarkably few degrees of data. Of course, all proteins and all twins aren't equal. So, don't expect to have varying twin fractions all the time.
Happy Refining, Chris On Tue, 17 Apr 2007, Mark Mayer wrote: >>>For cases where people have had merohedral twinning, did the twin fraction >>>vary substantially >>>between individual crystals grown under indentical conditions? I have no >>>prior experience with >>>merohedral twinning, and was surprised to see that the twin fraction varied >>>substantially as detailed >>>below, and that by screening we were able to get untwinned xtals. >>> >>>The project started with a weak home data set for which the twin fraction >>>was 0.478, and which >>>scaled in both H3 and H32. We just came back from APS with data sets from >>>another three crystals, >>>for which the ML twin fraction, estimated using phenix.xtriage with >>>scalepack merged intensities as >>>input, varied from 0.335, 0.219 and 0.02. The latter is refining very >>>nicely, in H3 and will not scale in >>>H32. >>> >>>Thanks - Mark >>> Christopher L. Colbert, Ph.D. Assistant Instructor Phone: (214) 645 5944 University of Texas Southwestern Medical Center FAX: (214) 645 5945 6001 Forest Park Lane Dallas, TX 75390
