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The ubiquitous, multi-enzyme, nucleotide excision repair (NER) pathway is responsible for correcting a wide range of chemically and structurally distinct DNA lesions in the eukaryotic genome. Human XPA, a 31 kDa, zinc-associated protein, is thought to play a major NER role in the recognition of damaged DNA and the recruitment of other proteins, including RPA, ERCC1, and TFIIH, to repair the damage. Sequence analyses and genetic evidence suggest that zinc is associated with a C4-type motif, C10S-X2-C108-X17-C126-X2-C129, located in the minimal DNA binding region of XPA (M98-F219). The zinc-associated motif is essential for damaged DNA recognition. Extended X-ray absorption fine structure (EXAFS) spectra collected on the zinc associated minimal DNA-binding domain of XPA (ZnXPA-MBD) show directly, for the first time, that the zinc is coordinated to the sulfur atoms of four cysteine residues with an average Zn-S bond length of 2.34 k 0.01 A. XPA-MBD was also expressed in minimal medium supplemented with cobalt nitrate to yield a blue-colored protein that was primarily (>95%) cobalt associated (CoXPA-MBD). EXAFS spectra collected on CoXPA-MBD show that the cobalt is also coordinated to the sulfur atoms of four cysteine residues with an average Co-S bond length of 2.33 k 0.02 A.Keywords: DNA repair protein; EXAFS; metalloproteins; nucleotide excision repair; XPA Nucleotide excision repair (NER) is a major cellular pathway for removing many structurally distinct DNA lesions from both prokaryotic and eukaryotic genomes (Friedberg et al

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The local atomic structure of CdTe:In at an In concentration of 6 at. % was investigated by x-ray absorption spectroscopy before and after photoexcitation at 80 K. After photoexcitation, In K edge spectra change in both the near-edge and x-ray absorption fine structure (XAFS) regions, showing a change in local structure. Cd and Te structural parameters are consistent with the structure of CdTe and did not change after photoexcitation. For In, only the first shell contribution is present in the XAFS, indicating a disordered environment beyond the first shell of neighbors. The relation of these observations with the proposed model of a DX center for CdTe:In is discussed.

We present a simplified model of electrons and phonons in a three-site cluster as a paradigm of a system exhibiting a lattice instability. We point out the utility of X-ray absorption fine structure (XAFS) in the study of materials where the coupling between electrons and phonons leads to the appearance of such lattice instabilities. As examples of these systems, we present X-ray absorption fine structure (XAFS) measurements on magnetic manganese oxide materials and II-VI semiconductors. Both of these systems exhibit local lattice instabilities which are reflected in the transport properties. In the case of the manganese oxide La0.67Ca0.33MnO3 we observe a change in the Mn-O local structure accompanying the ferromagnetic and metal-insulator transitions. For In doped CdTe we observe the appearance of a lattice distortion centered at the Cd atoms as the In concentration is increased. This distortion is associated with the trapping of free charge carriers, leading to the saturation of the conductivity as the In concentration increases.