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![[Figure 3]](yt5020fig3mag.jpg)
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Figure 3
Detection of twinning and estimation of the twin fraction α. Top row, cumulative intensity difference plot of the intensity difference of local pairs of intensities that are not twin-related |L| {L = [I(h1) − I(h2)]/[I(h1) + I(h2)]} against the cumulative probability distribution N(L) of the parameter L (Padilla & Yeates, 2003  ). The expected plots for untwinned and twinned acentric data (red) and the calculated plots for the SIVmac239 Nefcore–TCRζ polypeptide data (blue) are shown. Middle row, estimation of the twin fraction α by Britton plot analysis (Britton, 1972). The percentage of negative intensities after detwinning is plotted as a function of the assumed value of α. Overestimation of the twin factor α results in an increase in the percentage of negative intensities. The estimated value of α is extrapolated from the linear fit (dashed line). Bottom row, estimation of the twin fraction α using the H plot (Yeates, 1988). The cumulative fractional intensity difference of acentric twin-related intensities H {H = |I(h1) − I(h2)|/[I(h1) + I(h2)]} is plotted against H. The initial slope (dashed line) of the distribution is a measure of α. The expected slopes for the indicated twin fractions 0.0–0.4 are shown (dotted lines). |
![[Figure 3]](yt5020fig3.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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