UvrBC

UvrBC is a subcomplex of the bacterial nucleotide excision repair (NER) machinery, consisting of the UvrB helicase/translocase and the UvrC endonuclease. It forms during the repair process when the UvrA-UvrB damage-recognition complex binds to DNA damage, UvrA dissociates, and UvrC subsequently associates with UvrB to form the UvrBC complex. This complex executes the dual incisions that define the core step of bacterial NER.

The primary role of UvrBC is to introduce two incisions on the damaged strand, flanking the lesion. The 5' incision is typically made about 4–5 nucleotides upstream of the damage, while the 3' incision occurs roughly 8 nucleotides downstream. The resulting damaged DNA segment, commonly about 12–13 nucleotides in length, is then removed from the chromosome. After excision, repair synthesis fills the gap and DNA ligase seals the final nick.

Mechanistically, UvrB verifies and processes the damage through ATP-dependent translocation and DNA bending, while UvrC provides the endonuclease activity responsible for the incisions. The formation of the UvrBC complex is an intermediate step following the initial lesion recognition by UvrA and UvrB; later steps involve UvrD helicase–mediated removal of the excised segment and gap-filling synthesis.

Distribution and significance: UvrBC is a core component of bacterial NER, found in many bacteria such as Escherichia coli. It plays a critical role in removing bulky DNA adducts, ultraviolet-induced lesions, and other helix-distorting DNA damage, contributing to genomic stability and mutational control.