Biochemistry

Coordination Matters

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Science  20 Oct 2000:
Vol. 290, Issue 5491, pp. 409-411
DOI: 10.1126/science.290.5491.409e

Replication Protein A (RPA) binds to single-stranded DNA (ssDNA) and is involved in DNA replication, recombination, and repair. RPA contains a four-cysteine-type zinc-finger that is not essential for DNA binding. Instead the zinc-finger motif has been implicated in regulation of RPA function. Under oxidizing conditions, or in the presence of chelators of zinc, the DNA binding of RPA is impaired significantly.

Now You et al. have found that mutating any single zinc-binding cysteine has little effect upon DNA binding under reducing conditions, but prevents loss of DNA binding under oxidizing conditions. A mutant RPA protein lacking all four cysteines retained high-affinity binding to ssDNA independent of the prevailing redox conditions. Thus it appears that the zinc contributes to ssDNA-binding activity by preventing disulfide bond formation between the four coordinated cysteines. The authors suggest that the role of the zinc-finger is in redox regulation of RPA-ssDNA binding. Oxidation of the Zn(II) thiolate bond would lead to zinc release, resulting in the disulfide-bonded conformation of RPA that binds only weakly to ssDNA. Under reducing conditions, the cysteines would be coordinated by zinc to give the high-affinity ssDNA-binding conformation of RPA. — VV

Biochemistry, in press.

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