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![[Figure 2]](rr5135fig2mag.jpg)
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Figure 2
Detection of noncrystallographic symmetry in hlFBPase. (a) Superposition of the unique quarters of the u = 0 and u = 1/2 Patterson sections. The origin peak was removed and only peaks of >10σ are displayed. The u = 0 section (orange) contains a single non-origin peak at fractional coordinates (0, 0, 1/3) at a height of 31% of the origin peak. The peaks on the u = 1/2 (blue) section at fractional coordinates (1/2, 1/2, 1/6) and (1/2, 1/2, 1/2) have relative heights of 65 and 24%, respectively. Note that the peak at (1/2, 1/2, 1/6) is the sum of the vectors (1/2, 1/2, 1/2) and (0, 0, 1/3). The Patterson function was calculated to 2.5 Å resolution using XPREP (Bruker). (b) Stereographic projection of the κ = 180° section of the self-rotation function. Peaks occur at the expected positions for 422 symmetry. The function was calculated from data processed in space group P422 using XPREP (Bruker) with 10–2.5 Å resolution limits and a sphere radius of 55 Å. (c) Cumulative intensity distribution N(Z) of acentric reflections as a function of Z = I/〈I〉. hlFBPase data are drawn as a continuous blue line. Dashed lines represent the theoretical distributions for perfectly twinned (black) and untwinned (blue) data. The shift to larger N(Z) values indicates pseudo-translation, and possibly masks twinning. (d) L-test to detect the possible presence of twinning in the presence of pseudo-translation. The cumulative distributions and N(|L|) of the intensities I are plotted as a function of L = |I1 − I2|/(I1 + I2), where I1 and I2 are unrelated intensities (Padilla & Yeates, 2003  ). hlFBPase data are drawn as a continuous blue line, as in (c). Dashed lines are expected distributions for normal (blue) and perfectly twinned (black) data. The observed hlFBPase data show no strong deviations from the untwinned case. The mean value of |L| = 0.48 is close to that expected for un-twinned data (Table 1). The calculations in (c) and (d) were performed on data scaled in space group P4. Plots for data scaled in space group P422 look virtually identical. |
![[Figure 2]](rr5135fig2.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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