Final answer:
In E. coli nucleotide excision repair, UvrA and UvrB work together to detect DNA damage and initiate repair. UvrA scans for distortions, while UvrB creates a bubble at the damage site and recruits UvrC to excise the damaged DNA.
Step-by-step explanation:
In E. coli nucleotide excision repair, the enzymes UvrA and UvrB play crucial roles. UvrA initially scans the DNA for distortions indicating damage, such as thymine dimers, which are bulky lesions that distort the DNA helix. Once such damage is located, UvrA pairs with UvrB to form a complex that binds to the damaged DNA. UvrB has a further role where it induces the formation of a single-strand bubble around the site of damage. This is instrumental in the process because UvrB then recruits another enzyme, UvrC, which functions as an endonuclease, cutting out the damaged portion of the DNA strand.
The correct answer to the question is a. Scan DNA for distortions; UvrB (makes single-strand bubble) also recruits UvrC. This choice describes the role of UvrA and UvrB accurately, as they are directly involved in identifying and initiating repair of helix-distorting lesions through the nucleotide excision repair pathway.