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Nat Struct Mol Biol. 2006 Mar;13(3):278-84. Epub 2006 Feb 19.

Recognition of helical kinks by xeroderma pigmentosum group A protein triggers DNA excision repair.

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Institute of Pharmacology and Toxicology, University of Zürich-Vetsuisse, Winterthurerstrasse 260, CH-8057 Zürich, Switzerland.


The function of human XPA protein, a key subunit of the nucleotide excision repair pathway, has been examined with site-directed substitutions in its putative DNA-binding cleft. After screening for repair activity in a host-cell reactivation assay, we analyzed mutants by comparing their affinities for different substrate architectures, including DNA junctions that provide a surrogate for distorted reaction intermediates, and by testing their ability to recruit the downstream endonuclease partner. Normal repair proficiency was retained when XPA mutations abolished only the simple interaction with linear DNA molecules. By contrast, results from a K141E K179E double mutant revealed that excision is crucially dependent on the assembly of XPA protein with a sharp bending angle in the DNA substrate. These findings show how an increased deformability of damaged sites, leading to helical kinks recognized by XPA, contributes to target selectivity in DNA repair.

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