Supplementary Information

Table 1. Data collection and refinement statistics.

Space group P1

Unit cell parameters (Å)a =79.91, b =84.97, c =202.0

(º)α =90.36, β =92.97,  =109.94

Resolution (Å)40.0-2.9 (3.08 – 2.9)*

Reflections (Total/Unique)348602/108303

I/(I)15.2

Rmerge (%)7.6 (33.5)

Completeness (%)98.1 (94.5)

RefinementModel quality

Resolution (Å) 40.0 - 2.9 (3.08-2.9)RMSD bond length (Å)0.016§

Reflections used 108303(16822)RMSD bond angles (°)1.5

Rfactor(%) 23.6 (29.9) RMSD improper angles (°)1.09

Rfree(%) 28.4 (34.3)

Number of

Overall B-factor/RMSD (Å2) 71.3/1.5Ramachadran plot residues (%)

Number of protein atoms 26984 Most favorable regions84.4

Number of nucleic acid atoms 2802Allowed regions14.8

Number of water molecules¶ 1174 Generously allowed regions 0.8

Disallowed regions 0.1

Rmerge=hklj  Ij(hkl) - <I(hkl)> /hklj <I(hkl)>, where Ij(hkl) and <I(hkl)> are the intensity of measurement j and the mean intensity for the reflection with indices hkl, respectively. Rfactor, free=hklFcalc(hkl)  - Fobs(hkl) /hklFobs, where the crystallographic R-factor is calculated including and excluding reflections in the refinement. The free reflections constituted 4% of the total number of reflections. RMSD – root mean square deviation. I/(I) – ratio of mean intensity to a mean standard deviation of intensity. *The data for the highest resolution shell are shown in brackets. §A somewhat large RMSD obtained for bond length is probably related to the strong non-crystallographic symmetry restraints used, which resulted in considerable improvement of the R-free and Ramachadran plot during automatic refinement. ¶Water molecules were picked from the (Fobs-Fcalc) electron density maps at the 3 level using the automatic procedure implemented in the CNS program46 at the final stages of refinement The water molecules with electron density peaks less than 1.4 in the (2Fobs – Fcalc) electron density map were removed from the model.

NCS averaging.

While using the data obtained by summation and starting the averaging from initial MR phases, the correlation coefficients (CC, as implemented in the DM program) rapidly converged from 0.4 to 0.85 during the first few cycles at 4.0 Å resolution and then slowly converged to about 0.88 during the phase extension to 2.9 Å resolution. However, the phase extension beyond the 2.9 Å resolution resulted in a gradual divergence of CC up to the 0.7 level at 2.6 Å resolution. Using a similar procedure applied to the profile-fitted data, CC began to diverge from a resolution of about 3.8 Å to yield a substantially worse CC of 0.5 at 2.6 Å resolution. Therefore, the data obtained by summation were finally used in the refinement, and the resolution of data was limited to 2.9 Å as at higher resolution the intensities were probably still affected by twinning in spite of the large spot integration area.