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Figure 1.
Figure 1: Averaged side-view projections of HslVU complexes.
a-c, Electron micrographs of complexes formed in 50 mM Tris-
HCl, pH 7.5, 0.2 M KCl, 10 mM MgCl[2] and 1 mM ATP, representing
appropriate conditions for proteolytic activity. a, Negatively
stained molecules (ATP-  S
state; number of particles, N = 65; resolution, 32 Å). Note that
the proximal ring of HslU (arrowhead) is wider and more dense
than the outer ring (arrow); b, frozen-hydrated molecules (ATP-
S
state; N=250; resolution, 33 Å); c, frozen-hydrated molecules in
the AMP-PNP state, where AMP-PNP is an inactive ATP analogue (N
= 400; resolution, 33 Å). d-g, Side-view projections
calculated^6 from the crystal structure^2 but limited to 30 Å
resolution. Projections corresponding to different rotational
settings of the complex around the axis were averaged to give a
cylindrically averaged side view, as in the electron micrographs
(EMs). In d and e , HslU is in the opposite orientation from the
one in the crystal structure, whereas in f and g this
corresponds to the published orientation2. Projections shown in
e and g were created by applying a phase-contrast transfer
function (CTF; corresponding to 2.0  m
underfocus) to images in d and f , and so are more comparable to
the cryo-EMs. With or without CTF correction, it is evident that
the wider, denser ring, corresponding to the ATPase domains of
HslU, is adjacent to HslV. Arrows in e and c mark the axial
density that is missing in e but present in b and c, which we
attribute to residues 175 to 209. In e and g, I denotes the
I-domain ring, and A denotes the ATPase-domain ring. Scale bar,
100 Å.
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