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Figure 2
Deriving positions for the tungsten clusters in the crystal. (a) Anomalous difference Patterson map calculated for the peak data collected in cycle 1 [data between 10 and 5 Å with Fobs/σ(Fobs) > 5]. The Harker section w = 1/3 is shown and reveals strong Harker peaks as well as some cross-peaks. The positions for cluster 1 and 2 were found by hand using Harker peaks. Harker peaks for cluster 1 had a height of 26% of the origin (fortuitously high, as the position of cluster 1 resulted in the expected six Harker peaks overlapping to show only three peaks). Harker peaks for cluster 2 had a height of 17% of the origin. A number of strong cross-peaks are also seen in the Harker section w = 1/3. The position of cluster 3, first identified in an anomalous difference Fourier map, was confirmed with the anomalous difference Patterson map. (b) Anomalous difference Fourier map calculated with the peak-wavelength data set (cycle 1) from 15 to 6 Å and molecular-replacement phases (search model shown in yellow). Cluster 1 and 2 are found as electron-density peaks with the height of 6.5σ and 6.0σ, respectively; cluster 3 is weaker. The anomalous difference density was contoured at 4σ (shown in magenta for part of the unit cell). Cluster 3 is located on a crystallographic twofold axis lying along a diagonal between the a and b axes. The clusters 1 and 2 and half of cluster 3 fall within one asymmetric unit, while clusters 1′, 2′ and the other half of cluster 3 are located in another (indicated by white numbers).

Journal logoBIOLOGICAL
ISSN: 1399-0047
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