I once had a similar case, in which multiple lovely high-resolution data sets indexed very convincingly as body-centered orthorhombic, but had equally convincing absences of the form l=6n. I’ve not yet figured out this data set (the cell is too small for what we thought we were crystallizing, so there are multiple issues), but I’d love to hear a good explanation for the systematic absences.
Pat
> On 31 Aug 2016, at 5:48 AM, 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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