Sequence-specific interactions of UvrABC endonuclease with psoralen interstrand cross-links.

The nature of the Uvr protein-DNA complexes formed on psoralen-DNA interstrand cross-links was analyzed by DNase I footprinting and correlated with the incision efficiency of the UvrABC endonuclease on the cross-links of different DNA sequences. Our results indicate that the repair specificity is dependent on the DNA sequence and the psoralen orientation in the cross-link. On the strand that will be cut, a 30-nucleotide long UvrAB footprint with a DNase I hypersensitive site at the 11th nucleotide 5' to the lesion was observed and subsequently rearranged to a 22-nucleotide long UvrB-lesion footprint. On the strand that will not be cut, the UvrAB-lesion footprint had no 5' DNase I hypersensitive site and did not form the UvrB-lesion footprint. Although UvrABC incision requires the formation of UvrB-lesion complex on the strand which will be cut, the affinities of these complexes do not correlate with the incision efficiencies, suggesting that the overall reaction can be driven forward by a favorable next step such as UvrC incision. A study of the time-dependent interconversion of UvrAB-lesion complex to UvrB-lesion complex on a cross-link revealed a secondary recognition of the UvrB-lesion complex by UvrA2(B) proteins in vitro.