Uvr ABC Endonuclease - Mechanism

Mechanism

1. Two UvrA proteins form a dimer and they both have ATPase/GTPase activity.
2. The UvrA dimer binds with UvrB and forms a trimer that is able to detect DNA damage.The UvrA dimer functions as the unit responsible for the detection of DNA damage, probably through a mechanism of detecting distortions in the DNA double helix.
3. The UvrB part of the trimer attaches to the double helix at the damaged site.
4. The UvrA dimer leaves and a UvrC protein comes in and binds to the UvrB monomer and, hence, forms a new UvrBC dimer.
5. This dimer is responsible for cleaving the nucleotides either side of the DNA damage. UvrB cleaves a phosphodiester bond 4 nucleotides downstream of the DNA damage, and the UvrC cleaves a phosphodiester bond 8 nucleotides upstream of the DNA damage and created 12 nucleotide excised segment.
6. DNA helicase II (sometimes called UvrD) then comes in and removes the excised segment by removing the base pairing. The UvrB still remains in place even though UvrC has disassociated at this stage, as UvrB may be involved to prevent the reannealing of the excised DNA.
7. DNA polymerase I comes in and fills in the correct nucleotides sequence, kicking off UvrB in the process, and the last phosphodiester bond is completed by DNA ligase.