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S. Korolev, J. Hsieh, G. Gauss, T.M. Lohman, and G. Waksman.
Major domain swivelling revealed by the crystal structures of binary and
ternary complexes of Escherichia coli Rep helicase bound to single-stranded DNA and ADP.
Cell. 90:635-647. (1997)
Crystal structures of the E. coli Rep
helicase in a binary complex with single stranded (ss) DNA and in a ternary
complex with ss-DNA and ADP were determined to a resolution of 3.0 Angstroms
and 3.2 Angstroms, respectively. The asymmetric unit in the crystals of the
binary and ternary complexes contains two Rep monomers differing from each
other by a large reorientation of one of the domains, corresponding to a
swiveling of 130 degree about a hinge region. This large motion results in the
closing of a cleft involved in ss-DNA binding. Such domain movements, within
the context of the Rep dimer, are sufficiently large to suggest that these may
be coupled to translocation of the Rep dimer along DNA by a step-wise movement
of the subunits. The ss-DNA binding site involves the helicase motifs Ia, III,
and V, whereas the ADP binding site involves helicase motifs I and IV, such
that the ss-DNA binding and the ADP binding sites are non-overlapping. Residues
in motifs II and VI may function to transduce the allosteric effects of
nucleotides on DNA binding. These structures represent the first view of a DNA
helicase bound to DNA and also shed light on the regions of E. coli RecA
protein that interact with ss-DNA.