Dynamic in vivo interaction of DDB2 E3 ubiquitin ligase with UV-damaged DNA is independent of damage-recognition protein XPC.

Damage DNA binding protein 2 (DDB2) has a high affinity
for UV-damaged DNA and has been implicated in the initial
steps of global genome nucleotide excision repair (NER) in
mammals. DDB2 binds to CUL4A and forms an E3
ubiquitin ligase. In this study, we have analyzed the
properties of DDB2 and CUL4A in vivo. The majority of
DDB2 and CUL4A diffuse in the nucleus with a diffusion
rate consistent with a high molecular mass complex.
Essentially all DDB2 binds to UV-induced DNA damage,
where each molecule resides for ~2 minutes. After the
induction of DNA damage, DDB2 is proteolytically
degraded with a half-life that is two orders of magnitude
larger than its residence time on a DNA lesion. This
indicates that binding to damaged DNA is not the primary
trigger for DDB2 breakdown. The bulk of DDB2 binds to
and dissociates from DNA lesions independently of
damage-recognition protein XPC. Moreover, the DDB2-
containing E3 ubiquitin ligase is bound to many more
damaged sites than XPC, suggesting that there is little
physical interaction between the two proteins. We propose
a scenario in which DDB2 prepares UV-damaged
chromatin for assembly of the NER complex.