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Arabidopsis Cockayne Syndrome A-Like Proteins 1A and 1B Form a Complex with CULLIN4 and Damage DNA Binding Protein 1A and Regulate the Response to UV Irradiation
Caiguo Zhanga,b, Huiping Guoc, Jun Zhangb, Guangqin Guoa, Karen S. Schumakerd and Yan Guob,c,1
a Institute of Cell Biology, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
b National Institute of Biological Sciences, Beijing 102206, China
c State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100094, China
d Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721
In plants, as in animals, DNA is constantly subject to chemical modification. UV-B irradiation is a major genotoxic agent and has significant effects on plant growth and development. Through forward genetic screening, we identified a UV-B–sensitive mutant (csaat1a-3) in Arabidopsis thaliana, in which expression of CSAat1A, encoding a Cockayne Syndrome A-like protein, is reduced due to insertion of a T-DNA in the promoter region. Arabidopsis lacking CSAat1A or its homolog CSAat1B is more sensitive to UV-B and the genotoxic drug methyl methanesulfonate and exhibits reduced transcription-coupled repair activity. Yeast two-hybrid analysis indicated that both CSAat1A and B interact with DDB1A (UV-Damage DNA Binding Protein1). Coimmunoprecipitation assays demonstrated that CSAat1A and B associate with the CULLIN4 (CUL4)-DDB1A complex in Arabidopsis. A split-yellow fluorescent protein assay showed that this interaction occurs in the nucleus, consistent with the idea that the CUL4-DDB1A-CSA complex functions as a nuclear E3 ubiquitin ligase. CSAat1A and B formed heterotetramers in Arabidopsis. Taken together, our data suggest that the plant CUL4-DDB1ACSAat1A and B complex represents a unique mechanism to promote ubiquitination of substrates in response to DNA damage.
