Latency of transcription factor Stp1 depends on a modular regulatory motif that functions as cytoplasmic retention determinant and nuclear degron.
Bottom Line: Stp1, the effector transcription factor, is synthesized as a latent cytoplasmic precursor with an N-terminal regulatory domain that restricts its nuclear accumulation.Our results indicate that RI mediates latency by two distinct activities: it functions as a cytoplasmic retention determinant and an Asi-dependent degron.These findings provide novel insights into the SPS-sensing pathway and demonstrate for the first time that the inner nuclear membrane Asi proteins function in a degradation pathway in the nucleus.
Affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, S-106 91 Stockholm, Sweden.Show MeSH
Mentions: Next we asked whether the increased steady-state levels of RI15-35 and RI17-33 in asi1Δ cells—the consequence of enhanced stability in the absence of Asi1—could also be observed in cells lacking ASI2 or ASI3. Cells carrying deletions of ASI2 or ASI3 exhibit the same levels of Stp1/2-dependent promoter induction as asi1Δ mutants, and no additive effects are observed in cells carrying all possible double- and triple- mutant combinations (Zargari et al., 2007). We analyzed the steady-state amount of proteins in asi2Δ and asi3Δ cells in comparison to those in asi1Δ and ASI wild-type cells. Indeed, RI15-35 and RI17-33 proteins accumulated to the same extent in cells lacking any of the ASI genes compared with the amount detected in ASI wild-type cells (Figure 5A, compare lanes 2–4 with lane 1 and lanes 6–8 with lane 5). In conclusion, deletion of ASI1, ASI2, or ASI3 results in an identical phenotype; consequently, Asi1, Asi2, and Asi3 appear to contribute equally to maintaining Stp1 latency and do so by affecting levels of Stp1 in a RI-dependent manner.
Affiliation: Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, S-106 91 Stockholm, Sweden.