Roles of Rad23 protein in yeast nucleotide excision repair

Zhongwen Xie, Shuqian Liu, Yanbin Zhang, Zhigang Wang

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63 Scopus citations


Nucleotide excision repair (NER) removes many different types of DNA lesions. Most NER proteins are indispensable for repair. In contrast, the yeast Rad23 represents a class of accessory NER proteins, without which NER activity is reduced but not eliminated. In mammals, the complex of HR23B (Rad23 homolog) and XPC (yeast Rad4 homolog) has been suggested to function in the damage recognition step of NER. However, the precise function of Rad23 or HR23B in NER remains unknown. Recently, it was suggested that the primary function of RAD23 protein in NER is its stabilization of XPC protein. Here, we tested the significance of Rad23-mediated Rad4 stabilization in NER, and analyzed the repair and biochemical activities of purified yeast Rad23 protein. Cellular Rad4 was indeed stabilized by Rad23 in the absence of DNA damage. Persistent overexpression of Rad4 in rad23 mutant cells, however, largely failed to complement the ultraviolet sensitivity of the mutant. Consistently, deficient NER in rad23 mutant cell extracts could not be complemented by purified Rad4 protein in vitro. In contrast, partial complementation was observed with purified Rad23 protein. Specific complementation to the level of wild-type repair was achieved by adding purified Rad23 together with small amounts of Rad4 protein to rad23 mutant cell extracts. Purified Rad23 protein was unable to bind to DNA, but stimulated the binding activity of purified Rad4 protein to N-acetyl-2-aminofluorene-damaged DNA. These results support two roles of Rad23 protein in NER: (i) its direct participation in the repair biochemistry, possibly due to its stimulatory activity on Rad4-mediated damage binding/recognition; and (ii) its stabilization of cellular Rad4 protein.

Original languageEnglish
Pages (from-to)5981-5990
Number of pages10
JournalNucleic Acids Research
Issue number20
StatePublished - 2004

Bibliographical note

Funding Information:
We thank R. Daniel Gietz for the yeast expression plasmids Yeplac112, Yeplac195 and Yeplac181; Errol Friedberg for the yeast strains SX46A, BJ2168Drad2, SX46ADrad4 and SX46ADrad14; and Jaap Brouwer for the yeast strains W303-1B and MGSC101. This work was supported by a NIH grant CA67978.

ASJC Scopus subject areas

  • Genetics


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