Dear Genevieve,
With those cell dimensions, the 00l reflections are not the ones that you would expect to be pseudo-6-fold screw, because a is not similar to b.
Is it possible that you have translational non-crystallographic symmetry? Do you see a large off-origin peak in the native Patterson map? Programs like pointless, xtriage and Phaser will provide this information automatically. If so, that could lead to the apparent absences that you see.
Best wishes,
Randy Read
-----
Randy J. Read
Department of Haematology, University of Cambridge
Cambridge Institute for Medical Research Tel: +44 1223 336500
Wellcome Trust/MRC Building Fax: +44 1223 336827
Hills Road E-mail: [log in to unmask]
Cambridge CB2 0XY, U.K. www-structmed.cimr.cam.ac.uk
> On 31 Aug 2016, at 11:48, Genevieve Evans <[log in to unmask]> wrote:
>
> Hi All,
>
> I've been working with datasets for a protein crystal that I originally thought would be solved using MR, but so far I haven't been able to find a solution.
>
> There appears to be something not quite right about the space group.
>
> The highest symmetry Bravais Lattice with best quality of fit is oP (= orthorhombic primitive) with a unit cell of 29 92 94 90 90 90 in both XDS & iMosflm. POINTLESS auto-processes the datasets as P212121. However, in all the datasets I've worked on, the axial absences (from POINTLESS analysis) along one axis look more like 6-fold screw axis than a 2-fold screw axis .
>
> An example of this odd axial absences pattern from my best resolution dataset (AIMLESS, with conservative cut-off at 1.66 Angstrom, gives Rpim= 0.567 in outer shell & Rpim= 0.023 overall):
> Index I sigI I/sigI I'/sigI
> 1 -2 2 -0.94 0.47
> 2 4 2 1.61 1.96
> 3 4 3 1.36 1.67
> 4 5 4 1.11 1.50
> 5 3 5 0.68 0.00
> 6 5292 54 97.68 97.67
> 7 27 7 3.88 0.00
> 8 14 8 1.87 1.78
> 9 5 8 0.58 1.35
> 10 -7 8 -0.86 0.92
> 11 5 8 0.68 0.00
> 12 4126 43 96.33 96.32
> 13 18 18 1.04 0.00
>
> Additional when I look at the mtz file produced by AIMLESS, in reciprocal space using Phenix 2D map viewer, the data appears to have "stripes" in one direction, which correspond to this axis. I believe the stripes are due to the index numbers along one axis being 4-5 fold less than the index numbers along the other axes.
>
> Any ideas or suggestions? Perhaps someone else has come across a similar situation?
>
> Thanks,
> Genevieve
>
> Dr Genevieve Evans
> ------------------------
> School of Chemistry and Biochemistry
> The University of Western Australia (M310)
> 35 Stirling Highway
> CRAWLEY WA 6009
> Australia
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