FC0056
DNA helicase II UvrD  -  DNA

Biological function
UvrD (helicase II) is a superfamily 1A helicase that unwinds DNA during nucleotide excision repair (NER) and mismatch repair (MMR) in Gram-negative bacteria. During nucleotide excision repair (NER) in bacteria the UvrC nuclease and the short oligonucleotide that contains the DNA lesion are removed from the post-incision complex by UvrD, a superfamily 1A helicase. UvrD interacts with UvrB, a component of the post-incision complex.

Structural evidence
Using 2-hybrid analysis and surface plasmon resonance spectroscopy the N-terminal domain and the unstructured region at the C-terminus of UvrD was found to interact with UvrB. The truncated UvrD protein that lacked the unstructured C-terminal region showed a diminished affinity for single-stranded DNA, but retained the ability to displace both UvrC and the lesion- containing oligonucleotide from a post-incision nucleotide excision repair complex.

Biochemical evidence
The absence of the C-terminal extension in UvrD_1–647 reduced the apparent affinity of the protein for single- stranded DNA. Deletion either 40 or 102 residues from the C-terminus of E. coli UvrD (creating UvrDΔ40C and UvrDΔ102C) weakened binding to single-stranded DNA-cellulose columns, but in filter binding assays only UvrDΔ102C showed reduced affinity for single-stranded DNA. UvrDΔ40C, lost the ability to dimerise, but was otherwise functional: it retained helicase activity and the ability to restore the UV-resistance of a strain lacking uvrD. In contrast UvrDΔ102C lacked ATPase activity as well as DNA-binding ability.

Mechanism category
tethering

Significance
In Gram-positive organisms the roles of both UvrD and Rep are combined in a single essential helicase, PcrA, which can displace both UvrC and the damage-containing oligonucleotide from a post-incision NER complex. The fuzzy C-terminal region of UvrD, which interacts with UvrB could account for specificity, as Rep does not contain an equivalent C-terminal region, while PcrA does.