Mechanistic understanding of the Nucleotide Excision Repair: structural bases of damage detection process by UvrA and lesion hand-off to UvrB.

Nucleotide excision repair (NER) represents one of the major molecular machineries that control chromosome stability in all living species. In Eubacteria, the initial stages of the repair process are carried out by the UvrABC excinuclease complex. Despite the wealth of structural data available, some crucial details of the pathway remain elusive. In this study, we present a structural investigation of the Mycobacterium tuberculosis UvrA-UvrB complex and of the UvrA dimer, both in presence of damaged DNA. Our analyses have yielded new insights into the DNA binding mode of UvrA, as well as an unexplored conformation of some important regions involved in DNA coordination. Furthermore, we determined the molecular events related to the sequential binding of UvrB, leading to the formation of the uncharacterized UvrA ₂ UvrB-DNA and the UvrA ₂ UvrB ₂ -DNA complexes which we interpreted as hierarchical steps initiating the DNA repair cascade in NER pathway.