Exportin Crm1 is important for Swi6 nuclear shuttling and MBF transcription activation in Saccharomyces cerevisiae.

BACKGROUND: Swi6 acts as a transcription factor in budding yeast, functioning in two different heterodimeric complexes, SBF and MBF, that activate the expression of distinct but overlapping sets of genes. Swi6 undergoes regulated changes in nucleocytoplasmic localization throughout the cell cycle that correlate with changes in gene expression. This study investigates how nucleocytoplasmic transport by multiple transport factors may influence specific Swi6 activities. RESULTS: Here we show that the exportin Crm1 is important for Swi6 nuclear export and activity. Loss of a putative Crm1 NES or inhibition of Crm1 activity results in changes in nucleocytoplasmic Swi6 localization. Alteration of the Crm1 NES in Swi6 results in decreased MBF-mediated gene expression, but does not affect SBF reporter expression, suggesting that export of Swi6 by Crm1 regulates a subset of Swi6 transcription activation activity. Finally, alteration of the putative Crm1 NES in Swi6 results in cells that are larger than wild type, and this increase in cell size is exacerbated by deletion of Msn5. CONCLUSIONS: These data provide evidence that Swi6 has at least two different exportins, Crm1 and Msn5, each of which interacts with a distinct nuclear export signal. We identify a putative nuclear export signal for Crm1 within Swi6, and observe that export by Crm1 or Msn5 independently influences Swi6-regulated expression of a different subset of Swi6-controlled genes. These findings provide new insights into the complex regulation of Swi6 transcription activation activity and the role of nucleocytoplasmic shuttling in regulated gene expression.

Nuclear localisation is crucial for the proapoptotic activity of the HtrA-like serine protease Nma111p.

Programmed cell death is induced by the activation of a subset of intracellular proteins in response to specific extra- and intracellular signals. In the yeast Saccharomyces cerevisiae, Nma111p functions as a nuclear serine protease that is necessary for apoptosis under cellular stress conditions, such as elevated temperature or treatment of cells with hydrogen peroxide to induce cell death. We have examined the role of nuclear protein import in the function of Nma111p in apoptosis. Nma111p contains two small clusters of basic residues towards its N-terminus, both of which are necessary for efficient translocation into the nucleus. Nma111p does not shuttle between the nucleus and cytoplasm during either normal growth conditions or under environmental stresses that induce apoptosis. The N-terminal half of Nma111p is sufficient to provide the apoptosis-inducing activity of the protein, and the nuclear-localisation signal (NLS) sequences and catalytic serine 235 are both necessary for this function. We provide compelling evidence that intranuclear Nma111p activity is necessary for apoptosis in yeast.