The nuclear export of mRNA is a multi-step process that is mediated by proteins associated with mRNA. The formation of the mRNP begins by recruitment of mRNA export factors to the elongating transcripts followed by targeting of the mRNP to the nuclear pore complex (NPC). The mRNP-complex is than translocated through the NPC channel. Finally, the mRNP is disassembled in the cytoplasm, RNA is used for translation and export factors are returned to the nucleus for another round of mRNA export. Recently, we found that Dbp5 and Rad24 function in mediating mRNA export in S. pombe. Dbp5, an ATP-dependent helicase, is similar to the S. cerevisiae homolog and is essential for mRNA export. It is thought to function by disassembling the mRNP in the cytoplasm. Rad24, a member of the 14-3-3 family of repeat proteins, is a novel mRNA export factor. Our data shows that Rae1 associates with Dbp5, Rad24 and Dss1 to mediate nuclear export of mRNA export in S. pombe. We also found that Rae1, Dss1 and Rad24 in addition to being involved in mRNA export are also involved in monitoring DNA damage in G2 phase of the cell cycle. We found that in response to DNA damage, the mitotic activator Cdc25 is recruited to DNA damage sites along with Dss1-Rad24-Rae1. This recruitment of Cdc25 to DNA damage sites was dependent upon DNA-damage checkpoint protein Chk1. Based upon these results we have proposed a model in which the function of Cdc25 could be inhibited in the nucleus in response to DNA-damage via sequestration of the protein on DNA. Taken together, our data raises the possibility for coupling of the mRNA export and the DNA- damage process.

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National Cancer Institute (NCI)
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National Cancer Institute Division of Basic Sciences
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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