Abstract
Nucleotide excision repair (NER) is a versatile repair pathway which counteracts the deleterious effects of various DNA lesions such as UV-damage and numerous bulky chemical DNA adducts that interfere with base pairing and obstruct DNA replication and transcription. There are two pathways in NER: global genome repair (GGR) that surveys and removes the DNA damage on entire genome and transcription-coupled repair (TCR) that focuses on damage that blocks RNA polymerase IIo in transcription elongation. XAB2 (XPA-binding protein 2), consisting of 15 tetratricopeptide repeats (TPR), has been isolated by virtue of its ability to interact with xeroderma pigmentosum group A (XPA) protein, which has a crucial role at an early stage of NER. To further analyze the function of XAB2, we purified XAB2 as a multimeric protein complex from HeLa cells. The XAB2 complex consists of six subunits (hAquarius, XAB2, hPRP19, p50, hISY1 and PPIE) which appear to be involved in pre-mRNA splicing based on the function of yeast orthologues. Knockdown of XAB2 with siRNA in HeLa cells resulted in a hypersensitivity to killing by UV or mitomycin C, and a decrease of recovery of RNA synthesis after UV-irradiation, RNA synthesis itself and pre-mRNA splicing. The amount of XAB2 protein bound to RNA polymerase IIo or XPA was increased in the cells treated with DNA damaging-agents that are subjected to NER, indicating a DNA damage-responsive activity of XAB2. These results suggested that the XAB2 complex is involved in transcription elongation and pre-mRNA splicing, and in TCR by the recruitment of CSA, CSB and XPA to the DNA damage sites where RNA polymerase IIo is stalled.
