Affiliation:
1. Ludwig Institute for Cancer Research, Stockholm, Sweden
Abstract
ABSTRACT
Stp1p and Stp2p are homologous and redundant transcription factors that are synthesized as latent cytoplasmic proteins with N-terminal regulatory domains. In response to extracellular amino acids, the plasma membrane-localized Ssy1p-Ptr3p-Ssy5p (SPS) sensor induces an endoproteolytic processing event that cleaves away the N-terminal regulatory domains. The shorter forms of Stp1p and Stp2p are targeted to the nucleus, where they bind and activate the transcription of amino acid permease genes. A novel genetic screen, specifically designed to search for rare mutations that affect the SPS-sensing pathway, identified the F-box protein Grr1p as an obligatory factor required for Stp1p/Stp2p processing. Additionally, we have found that a null mutation in the
ASI1
(amino acid sensor-independent) gene enables full-length unprocessed Stp1p/Stp2p to enter the nucleus and derepress SPS sensor-dependent genes. The N-terminal domains of Stp1p/Stp2p contain two conserved motifs that are required for proper nuclear exclusion and proteolytic processing. These motifs function in parallel; mutations that abolish processing inhibit signaling, whereas mutations that interfere with cytoplasmic retention result in constitutive derepression of SPS sensor-regulated genes independently of processing. The N-terminal domain of Stp1p is functionally autonomous and transferable to other transcription factors, where its presence confers
ASI1
-dependent nuclear exclusion and SPS sensor-induced proteolytic processing.
Publisher
American Society for Microbiology
Subject
Cell Biology,Molecular Biology
Cited by
44 articles.
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