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Abstract
The xeroderma pigmentosum complementation group B (XPB) protein is involved in both
DNA repair and transcription in human cells. It is a component of the transcription
factor IIH (TFIIH) and is responsible for DNA helicase activity during nucleotide
(nt) excision repair (NER). Its high evolutionary conservation has allowed identification
of homologous proteins in different organisms, including plants. In contrast to other
organisms, Arabidopsis thaliana harbors a duplication of the XPB orthologue (AtXPB1
and AtXPB2), and the proteins encoded by the duplicated genes are very similar (95%
amino acid identity). Complementation assays in yeast rad25 mutant strains suggest
the involvement of AtXPB2 in DNA repair, as already shown for AtXPB1, indicating that
these proteins may be functionally redundant in the removal of DNA lesions in A. thaliana.
Although both genes are expressed in a constitutive manner during the plant life cycle,
Northern blot analyses suggest that light modulates the expression level of both XPB
copies, and transcript levels increase during early stages of development. Considering
the high similarity between AtXPB1 and AtXPB2 and that both of predicted proteins
may act in DNA repair, it is possible that this duplication may confer more flexibility
and resistance to DNA damaging agents in thale cress.