The UvrABC repair system catalyzes the recognition and processing of DNA lesions. A damage recognition complex composed of 2 UvrA and 2 UvrB subunits scans DNA for abnormalities. Upon binding of the UvrA(2)B(2) complex to a putative damaged site, the DNA wraps around one UvrB monomer. DNA wrap is dependent on ATP binding by UvrB and probably causes local melting of the DNA helix, facilitating insertion of UvrB beta-hairpin between the DNA strands. Then UvrB probes one DNA strand for the presence of a lesion. If a lesion is found the UvrA subunits dissociate and the UvrB-DNA preincision complex is formed. This complex is subsequently bound by UvrC and the second UvrB is released. If no lesion is found, the DNA wraps around the other UvrB subunit that will check the other stand for damage. Forms a heterotetramer with UvrA during the search for lesions. Interacts with UvrC in an incision complex. The beta-hairpin motif is involved in DNA binding. This bacteria is considerably more resistant to UV and gamma irradiation than E.coli; the E.coli-like SOS regulon model is not an appropriate model for DNA repair in this cyanobacterium. Belongs to the UvrB family.