ABSTRACT
Target of rapamycin complex 1 (TORC1) is activated in response to nutrient availability and growth factors, promoting cellular anabolism and proliferation. To explore the mechanism of TORC1-mediated proliferation control, we performed a genetic screen in fission yeast and identified Sfp1, a zinc-finger transcription factor, as a multicopy suppressor of temperature-sensitive TORC1 mutants. Our observations suggest that TORC1 phosphorylates Sfp1 and protects Sfp1 from proteasomal degradation. Transcription analysis revealed that Sfp1 positively regulates genes involved in ribosome production together with two additional transcription factors, Ifh1/Crf1 and Fhl1. Ifh1 physically interacts with Fhl1, and the nuclear localization of Ifh1 is regulated in response to nutrient levels in a manner dependent on TORC1 and Sfp1. Taken together, our data suggest that the transcriptional regulation of the genes involved in ribosome biosynthesis by Sfp1, Ifh1, and Fhl1 is one of the key pathways through which nutrient-activated TORC1 promotes cell proliferation.
Subject(s)
Saccharomyces cerevisiae Proteins , Schizosaccharomyces , Transcription Factors/genetics , Transcription Factors/metabolism , Saccharomyces cerevisiae Proteins/genetics , Saccharomyces cerevisiae Proteins/metabolism , Saccharomyces cerevisiae/metabolism , Schizosaccharomyces/genetics , Schizosaccharomyces/metabolism , Mechanistic Target of Rapamycin Complex 1/metabolism , DNA-Binding Proteins/genetics , DNA-Binding Proteins/metabolism , Ribosomes/metabolism , Cell Proliferation , Gene Expression Regulation, FungalABSTRACT
Mammalian target of rapamycin complex 1 (TORC1) is controlled by the GATOR complex composed of the GATOR1 subcomplex and its inhibitor, the GATOR2 subcomplex, sensitive to amino acid starvation. Previously, we identified fission yeast GATOR1 that prevents deregulated activation of TORC1 (Chia et al., 2017). Here, we report identification and characterization of GATOR2 in fission yeast. Unexpectedly, the GATOR2 subunit Sea3, an ortholog of mammalian WDR59, is physically and functionally proximal to GATOR1, rather than GATOR2, attenuating TORC1 activity. The fission yeast GATOR complex is dispensable for TORC1 regulation in response to amino acid starvation, which instead activates the Gcn2 pathway to inhibit TORC1 and induce autophagy. On the other hand, nitrogen starvation suppresses TORC1 through the combined actions of the GATOR1-Sea3 complex, the Gcn2 pathway, and the TSC complex, another conserved TORC1 inhibitor. Thus, multiple, parallel signaling pathways implement negative regulation of TORC1 to ensure proper cellular starvation responses.
Subject(s)
Mechanistic Target of Rapamycin Complex 1/genetics , Schizosaccharomyces pombe Proteins/genetics , Schizosaccharomyces/genetics , Signal Transduction , Mechanistic Target of Rapamycin Complex 1/metabolism , Schizosaccharomyces/metabolism , Schizosaccharomyces pombe Proteins/metabolismABSTRACT
A novel polyhydroxyalkanoate (PHA)-producing bacterium, Jeongeupia sp. USM3 (JCM 19920) was isolated from the limestone soil at Gua Tempurung, Perak, Malaysia. This is the first report on the complete genome sequence for the genus Jeongeupia. This genome consists of a circular chromosome with a size of 3,788,814 bp and contains 3557 genes. Two PHA synthase (phaC) genes encoding for the key enzyme in the polymerization of PHA monomers and other PHA-associated genes were identified from the genome. Phylogenetic analysis of the PhaC protein sequences has revealed that both PhaC1 and PhaC2 of Jeongeupia sp. USM3 are categorized as Class I PHA synthases with 56% similarity to each other. Both of the PHA synthase genes of this isolate were cloned and heterologously expressed in a PHA mutant strain Cupriavidus necator PHB-4. The ability of the transformants to accumulate PHA showed that both PhaC1 and PhaC2 were functional.
Subject(s)
Acyltransferases/metabolism , Betaproteobacteria/enzymology , Betaproteobacteria/genetics , Genome, Bacterial , Polyhydroxyalkanoates/biosynthesis , Soil Microbiology , Acyltransferases/genetics , Cupriavidus necator/genetics , Malaysia , Phylogeny , Whole Genome SequencingABSTRACT
PHA synthase (PhaC) is the key enzyme in the production of biodegradable plastics known as polyhydroxyalkanoate (PHA). Nevertheless, most of these enzymes are isolated from cultivable bacteria using traditional isolation method. Most of the microorganisms found in nature could not be successfully cultivated due to the lack of knowledge on their growth conditions. In this study, a culture-independent approach was applied. The presence of phaC genes in limestone soil was screened using primers targeting the class I and II PHA synthases. Based on the partial gene sequences, a total of 19 gene clusters have been identified and 7 clones were selected for full length amplification through genome walking. The complete phaC gene sequence of one of the clones (SC8) was obtained and it revealed 81% nucleotide identity to the PHA synthase gene of Chromobacterium violaceum ATCC 12472. This gene obtained from uncultured bacterium was successfully cloned and expressed in a Cupriavidus necator PHB(-)4 PHA-negative mutant resulting in the accumulation of significant amount of PHA. The PHA synthase activity of this transformant was 64 ± 12 U/g proteins. This paper presents a pioneering study on the discovery of phaC in a limestone area using metagenomic approach. Through this study, a new functional phaC was discovered from uncultured bacterium. Phylogenetic classification for all the phaCs isolated from this study has revealed that limestone hill harbors a great diversity of PhaCs with activities that have not yet been investigated.
