Ste11p, a High-Mobility-Group Box DNA-Binding Protein, Undergoes Pheromone- and Nutrient-Regulated Nuclear-Cytoplasmic Shuttling

Abstract

The high-mobility-group (HMG) box is a conserved DNA-binding domain found in a family of transcription factors that regulate growth and development. One family member, Ste11p, directs sexual differentiation of Schizosaccharomyces pombe by binding specific DNA sequences upstream of genes required for mating and meiosis. Here, we show that Ste11p is a shuttling protein. In growing cells, Ste11p is present in low levels and is pancellular. Mating pheromones and nutrient limitation trigger nuclear accumulation and increased expression of the transcription factor. Several mechanisms likely control Ste11p localization. First, the 14-3-3 protein, Rad24p, binds phosphorylated Ste11p and inhibits its nuclear accumulation. Second, the HMG domain of Ste11p contains a basic cluster nuclear localization signal. Finally, treatment of cells with leptomycin B, an exportin inhibitor, results in the nuclear accumulation of Ste11p. A Ste11p deletion mutation, ⌬C54, mimics the effects of leptomycin B. The C54 region contains no identifiable nuclear export signal but instead is required for biological activity and to stimulate Ste11p target gene expression. These results provide evidence that both nuclear import and export mechanisms operate to regulate cellular localization of an HMG box protein. In addition, they establish a paradigm for the potential role of pheromone/hormone-like polypeptides in cellular localization of this important class of developmental regulators.

Discovery of parasite virulence genes reveals a unique regulator of chromosome condensation 1 ortholog critical for efficient nuclear trafficking

“…We have shown here that the TgRCC1 mutant is defective in nuclear trafficking. Many model organisms rapidly transport regulatory molecules into and out of the nucleus during nutrient limitation (30)(31)(32)(33). Our data suggest that T. gondii needs to efficiently traffic molecules into and out of the nucleus under nutrient deprivation, and that serum starvation in cell culture mimics at least some of the conditions that T. gondii encounters in vivo.…”

“…In response to nutrient limitation, many organisms traffic mRNA and regulatory proteins such as transcription factors, kinases, and RNA binding proteins into and out of the nucleus (30)(31)(32)(33). Given that the 73F9 mutant has a reduced amount of TgRCC1 protein and RCC1 proteins are known to play critical roles in maintaining the proper gradients essential for nucleocytoplasmic transport, we examined nuclear trafficking in the 73F9 mutant.…”

Global roles of Ste11p, cell type, and pheromone in the control of gene expression during early sexual differentiation in fission yeast

“…The mechanism by which pheromone enhances Ste11p activity is only partly understood: Ste11p is phosphorylated by the MAP kinase of the pheromone pathway (Spk1p) (27), and pheromone signaling leads to an increase in the concentration of Ste11p in the nucleus (28). Interestingly, ste11 overproduction results in the induction of all Ste11p targets, including those that are normally absolutely dependent on pheromone for their transcription (Fig.…”

Truncated Sla1 Induces Haploid Meiosis through the Pat1-Mei2 System in Fission Yeast

“…As the result, in transformants harboring pSLF173 or pSLF173-sla1FL, GFP-Ste11 localized all over the cell and its fluorescence was very weak in this condition, as reported before. 9) In contrast to this observation, GFP-Ste11 co-expressed with Sla1ÁC accumulated in the nucleus even in the nutrient rich medium (Fig. 3(A)).…”

“…9) We thought that if Pat1 was inactivated by Sla1ÁC, Ste11 must localize to the nucleus. To confirm this hypothesis, pSLF173-Sla1FL and pSLF173-Sla1ÁC were constructed as follows.…”