The nuclear export of mRNA is mediated by proteins that are associated with it in the nucleus. Export factors are recruited to the RNA during transcriptional elongation. Some of the proteins associated with the mRNA, target the mRNP to the NPC for export out of the nucleus. In the cytoplasm the mRNP is disassembled, RNA is used for translation and the proteins are returned to the nucleus. Recently, using tandem affinity purification (TAP) of genomic tagged rae1, we identified several nuclear pore proteins that associate with Rae1 in fission yeast. We found S. pombe Nup189, Nup186, Nup184, Nup170, Nup146, Nup132, Nup124, Nup120, Nup107, Npp106, Nup97, Nup61, Nup45, Nup44, Nup40 and Nsp1 co-purified with TAP tagged Rae1. In budding yeast these above NPC proteins have been found to form several NPC-protein complexes, some involved with nuclear export and some with nuclear import. Our data would indicate that Rae1p appears to be associated with several NPC-complexes during the nucleocytoplasmic exchange process. Additionally, we found that Dss1p a DNA repair and mRNA export factor, along with mitotic activator Cdc25p, messenger RNA export/cell cycle factor Rae1p, 19 S proteasomal factors, and recombination protein Rhp51p (a Rad51p homolog) copurified with a DNA-damage checkpoint protein TAP tagged Rad24, a member of the 14-3-3 family of proteins . Using chromatin immunoprecipitation, we found that Dss1p recruited Rad24 and Rae1 to the double-strand break (DSB) sites. Furthermore, Cdc25 also recruited to the DSB site, and its recruitment was dependent on Dss1, Rad24, and the protein kinase Chk1. Following DSB, all nuclear Cdc25 was found to be chromatin-associated. We found that Dss1 and Rae1 have a DNA damage checkpoint function, and upon treatment with UV light a null strain of dss1 cells entered mitosis prematurely with indistinguishable timing from the null rad24 cells. Taken together, these results suggest that Dss1 plays a critical role in linking repair and checkpoint factors to damaged DNA sites by specifically recruiting Rad24 and Cdc25 to the DSBs. We have suggested that the sequestration of Cdc25 to DNA damage sites could provide a mechanism for S. pombe cells to arrest at G2/M boundary in response to DNA damage. The involvement of mRNA export factors in multiple cellular processes raises the possibility that mRNA export and the DNA-damage/ cell cycle processes may be linked.
| Selvanathan, Saravana P; Thakurta, Anjan G; Dhakshnamoorthy, Jothy et al. (2010) Schizosaccharomyces pombe Dss1p is a DNA damage checkpoint protein that recruits Rad24p, Cdc25p, and Rae1p to DNA double-strand breaks. J Biol Chem 285:14122-33 |
