Nuclear pores mediate the transport of proteins and RNA between the nucleus and cytoplasm in a bi-directional fashion. Genetic screens in yeast have been used to identify mutations in genes whose products influence the export of mRNA out of the nucleus. We have used fission yeast Schizo saccharomyces pombeas a model system to study nucleocytoplasmic trafficking. We have identified temperature sensitive mutant of S. pombe rae1-1 that rapidly accumulates mRNA in the nucleus and undergoes a cell cycle arrest at the G2/M boundary upon shift to restrictive temperature. The RAE1 gene is highly conserved in evolution, and the human RAE1 gene can functionally complement the S. pombe rae1-1 mutation. In S. pombe Rae1p localizes to the nuclear periphery with appearance similar to staining observed for nuclear pores. There is also some staining in the cytoplasm. To identify genes that genetically and functionally interact with rae1 in mRNA export, we developed a synthetic lethal screen with a conditional mRNA export allele, rae1-167. Mutations defining three complementation groups were identified. The rae1- 167 mutation was synthetically lethal with a mutation in the non-repeat nucleoporin npp106, whose predicted protein shares significant similarity to the non-repeat nucleoporin of S. cerevisiae, Nic96. Additionally, the rae1-167 mutation was synthetically lethal with another nucleoporin, nup188. A consequence of the synthetic lethality between rae1-167 mutation and a mutation in npp106 or nup188 is accumulation of mRNA in the nucleus. Our results uncover involvement of Npp106p and Nup188p in mRNA export. In addition to the involvement of Nup188p in mRNA export, it is required for maintaining the integrity of the nuclear membrane and for proper DNA segregation of S. pombe cells. Several suppressors of the rae1-167 nup188-1 synthetic lethality were isolated that restored mRNA export under synthetic lethal conditions. One of them encodes a protein with RNA binding domains. This protein primarily localizes to the cytoplasm but upon inactivation of rae1 function accumulates in the nucleus. Moreover, it physically interacts with Rae1p. These and other observations have led us to identify components of the mRNA export machinery, some of which have additional role in cell cycle progression.
| Thakurta, Anjan G; Gopal, Ganesh; Yoon, Jin Ho et al. (2004) Conserved nuclear export sequences in Schizosaccharomyces pombe Mex67 and human TAP function in mRNA export by direct nuclear pore interactions. J Biol Chem 279:17434-42 |
