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Figure 2.
Figure 2. Comparison of the conformations of the Lac repressor
bound to operator and inducer. a, Stereo C  superposition
showing the difference in NH[ 2]-subdomain orientation in the
structure of the Lac repressor bound to operator (red) and to
IPTG (blue). The least squares superposition minimized the
r.m.s.d. of the C atoms
of only the CO[2]-subdomains of the core of the repressor (not
the NH[2]-subdomains). Residues 1 -61 of the repressor bound to
IPTG (not shown) are, in the absence of operator, not seen in
structures and are presumed to be mobile with respect to the
core. b, Stereo C superposition
of an individual NH[2]-subdomain in the structures of the
repressor bound to operator (red) and IPTG (blue). Residues for
which the largest structural differences occur (>4.5 Å), notably
Arg 101, are shown in ball-and-stick representation. Differences
in all of these residues arrise from different interactions at
the dimer interface in the IPTG-bound and operator-bound
conformations of the repressor.
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