The Rpt6 protein has been found to associate with a number of activators and to be localized on some promoters in mammals. In particular, Rpt6 has http://www.selleckchem.com/products/INCB18424.html been localized on p21WAF1 promoter where it interacts with p53 after DNA damage. The knockdown of Rpt6 results in increased occupancy of the p21WAF1 promoter by p53 and increase transcription of the gene. Modulation of Ub proteasome genes by cisplatin We previously studied genome wide transcriptional pro files in S. pombe, demonstrating that cisplatin activates a stress response involving genes belonging to different pathways, includ ing Ub proteasome system. In such an analysis, the S. pombe wild type sensitive strain 972 h was exposed to a cytotoxic cisplatin concentration and modulation of gene expression was examined.

The group of transcripts at least two fold up regulated by cisplatin in this strain comprised a subset of transcripts belonging to the Ub proteasome pathway. Only three of them were found to be included in the present set of non essential deletion mutants. When we tested cisplatin sensitivity of these specific deletion mutants, we obtained IC50 values similar to that of the corresponding wild type parental strain. Among the induced transcripts, Lub1 attracted our attention because a precise and important role in DNA damage response has been recently ascribed to its corre sponding budding yeast homolog gene, DOA1 UFD3. In particular, DOA1 has been shown to help to control the DNA damage response by channelling Ub from the proteasomal degradation pathway into path ways that mediate altered DNA replication and chroma tin modification, thus acting in supplying Ub for the DNA damage response.

Elements of the DNA damage response that appear to rely on DOA1 include the ubi quitination of both PCNA and histone H2B. Indeed, DOA1 interacts with other factors involved in producing or maintaining ubiquitinated both PCNA and H2B, i. e. UBC13 and UBP10. Thus, such an observation suggests a link between three differ ent factors belonging to the Ub proteasome pathway identified in S. pombe with two different approaches, and possibly involved in cellular response to cisplatin. Moreover, the lack of cisplatin hypersensitivity observed in our Lub1 deletion mutant, may reflect the presence of redundant factors as sug gested by Lis and Romesberg.

Indeed, in budding yeast doa1 and ubi4 mutants share several pheno types including sensitivity to heat, canavanine Brefeldin_A and other DNA damaging agents. In contrast, the budding yeast UBI4 deletion mutant displays resistance to cisplatin together with other mutants of the protea some pathway including BUL1, UBP13, UFD4 and UMP1. Both UBI4 and DOA1 might supply Ub for the DNA damage response. Similarly, in fission yeast the corre sponding UBI4 homolog gene may replace Lub1 absence. Accordingly, Ubi4 gene expression resulted up regulated by cisplatin in our previous study, similarly to Lub1. As reported in Table 4, the human ortholog of S.