The transient opening of the DNA double helix is a fundamental step in several DNA metabolic processes. This reaction is driven by proteins called helicases, which make use of ATP as fuel to unwind the DNA duplex. The RecQ family of helicases helps maintain genome stability. Recent studies have shown that RecQ helicases, in addition to promoting DNA unwinding, can also catalyze the opposite reaction: the pairing of the partially unwound DNA duplexes. The mechanisms underlying the regulation of this dual enzymatic activity are unknown, however.
In a new study published online in the open access journal PLoS Biology, Laura Muzzolini, Alessandro Vindigni, and colleagues describe two structural forms of the human RECQ1 helicase, a large oligomeric complex composed of five or six subunits and a smaller form consistent with only one or two molecules. An initial view of the three-dimensional structure of the larger complex is provided, including a demonstration that this state is associated with DNA strand annealing, whereas the smaller form carries out DNA unwinding. The functional switch from strand-annealing to DNA unwinding is controlled by ATP binding, which promotes the dissociation of the larger, higher-order complexes. By providing insight into the mechanisms regulating RecQ helicase activity, this study opens a new window into a fundamental aspect of DNA metabolism.
Citation: Muzzolini L, Beuron F, Patwa rdhan A, Popuri V, Cui S, et al. (2007) Different quaternary structures of human RECQ1 are associated with its dual enzymatic activity.
PLoS Biol 5(2): e20. doi:10.1371/journal.pbio.0050020.
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