The RAD10 gene of Saccharomyces cerevisiae is one of at least five genes required for damage-specific incision of DNA during nucleotide excision repair. This gene was previously cloned and sequenced [Weiss, W. A., & Friedberg, E. C. (1985) EMBO J. 4, 1575–1582; Reynolds et al. (1985) EMBOJ. 4, 3549–3552]. In the present studies, we have mapped one major and three minor transcriptional start sites in the RADIO gene. The locations of these sites relative to the translational start codon are remarkably similar to those previously identified in the yeast RAD2 gene [Nicolet et al. (1985) Gene 36, 225–234]. The two genes also share common sequences in these regions. However, in contrast to RAD2 [Robinson et al. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 1842–1846], RADIO is not induced following exposure of cells to the DNA-damaging agent 4-nitroquinoline 1-oxide. Native Radl0 protein and also two different Rad10 fusion proteins are rapidly degraded in most Escherichia coli strains. However, following overexpression of the cloned RADIO gene in yeast, native Radl0 protein was purified to >90% homogeneity. A catalytic function has not been identified for the purified protein. RADIO cells (untransformed with the cloned gene) contain fewer than 500 molecules per cell. This is similar to the levels of the UvrA, UvrB, and UvrC nucleotide excision repair proteins in E. coli.
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