Table I. Crystallographic statistics.

Resolution range	100–3.2 Å	(3.26–3.2 Å)
No. of reflections measured	503 540
No. of unique reflections	189 615	(6632)
Completeness	89.1%	(62.9%)
Rmergea	0.112	(0.331)
I/σ(I)	7.0	(1.9)
R-factorb	0.263	(0.345)
Rfreec	0.308	(0.411)
R.m.s. bond lengthsd	0.009 Å
R.m.s. bond anglesd	1.391°
Average B-factor: proteasome	64.7 Å2
Average B-factor: PA26	95.9 Å2

The data used are those of Whitby et al. (2000). Slight improvements have been made throughout the model by further refinement, especially for the N-terminal residues of α-subunits, which were visualized following non-crystallographic symmetry averaging in the proteasome gate region as described in the text. Values in parentheses refer to the highest resolution shell.

^aR_merge = Σ|I – <I>|/ΣI, where I is the intensity of an individual measurement and <I> is the corresponding mean value.

^bR-factor = Σ||F_o| – |F_c||/Σ|F_o|, where |F_o| is the observed and |F_c| the calculated structure factor amplitude.

^cR_free is the same as R_factor calculated with a randomly selected test set of 1264 reflections that were never used in refinement calculations.

^dThe r.m.s. deviation in bond lengths and bond angles from ideal values.