Cross-linking studies with the uvrA and uvrB proteins of E. coli.

The interactions of the uvrA and uvrB proteins with DNA have been investigated using a DNA-protein cross-linking technique. It is demonstrated that hydrolysis of ATP by the uvrA protein facilitates cross-linking of this protein to single-stranded DNA, whether the DNA is UV irradiated or not. In contrast, cross-linking to unirradiated double-stranded DNA is not facilitated by ATP hydrolysis and is in fact increased by the substitution of the non-hydrolysable analogue aTP gamma S for ATP. In the presence of ATP, a dose-dependent increase is observed in the amount of uvrA protein which can be cross-linked to UV-irradiated double-stranded DNA. Binding of uvrB protein to puvrA-DNA complexes has a stabilising effect and increases the number of complexes which can be cross-linked whether the substrate is single- or double-stranded DNA. We can find no evidence that ATP hydrolysis by uvrA protein results in unwinding of UV-damaged DNA.