Roles of Dhh1 RNA helicase in yeast filamentous growth: Analysis of N-terminal phosphorylation residues and ATPase domai
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Roles of Dhh1 RNA helicase in yeast filamentous growth: Analysis of N-terminal phosphorylation residues and ATPase domains Eunji Lee, Daehee Jung, and Jinmi Kim* Department of Microbiology and Molecular Biology, College of Bioscience and Biotechnology, Chungnam National University, Daejeon 34134, Republic of Korea (Received Aug 18, 2020 / Revised Sep 3, 2020 / Accepted Sep 8, 2020)
In yeast Saccharomyces cerevisiae, the Dhh1 protein, a member of the DEAD-box RNA helicase, stimulates Dcp2/Dcp1mediated mRNA decapping and functions as a general translation repressor. Dhh1 also positively regulates translation of a selected set of mRNAs, including Ste12, a transcription factor for yeast mating and pseudohyphal growth. Given the diverse functions of Dhh1, we investigated whether the putative phosphorylation sites or the conserved motifs for the DEADbox RNA helicases were crucial in the regulatory roles of Dhh1 during pseudohyphal growth. Mutations in the ATPase A or B motif (DHH1-K96R or DHH1-D195A) showed significant defects in pseudohyphal colony morphology and agar invasive phenotypes. The N-terminal phospho-mimetic mutation, DHH1-T16E, showed defects in pseudohyphal phenotypes. Decreased levels of Ste12 protein were also observed in these pseudohyphal-defective mutant cells under filamentous-inducing low nitrogen conditions. We suggest that the ATPase motifs and the Thr16 phosphorylation site of Dhh1 are crucial to its regulatory roles in pseudohyphal growth under low nitrogen conditions. Keywords: pseudohyphal growth, Dhh1, Ste12 expression, ATPase domain, phosphorylation Introduction The budding yeast Saccharomyces cerevisiae can undergo a dimorphic transition from yeast to pseudohyphal growth upon nitrogen or glucose limitation (Gimeno et al., 1992; Liu et al., 1996). The cells elongate and form multicellular filaments, which superficially resembles the true hyphae of filamentous fungi. Pseudohyphal formation is highly regulated by several signaling pathways, including the cAMP-dependent protein kinase (PKA) pathway and the mitogen-activated protein kinase (MAPK) pathway (Liu et al., 1993; Gancedo, 2001). The MAPK cascade of Ste11, Ste7, and Kss1 activates pseudohyphal growth through transcription factors Ste12 and *For correspondence. E-mail: [email protected]; Tel.: +82-42-821-6416; Fax: +82-42-822-7367 Copyright G2020, The Microbiological Society of Korea
Tec1. The PKA pathway involves transcription factors Flo8 and Sfl1. In addition, the nutrient-sensing TOR (target of rapamycin) pathway regulates pseudohyphal growth through the Gcn4 factor (Braus et al., 2003; Mutlu et al., 2019). These signaling pathways control the transcription of a number of filamentation-specific genes, including FLO11. Filamentation in S. cerevisiae is an informative model of hyphal growth in human pathogenic yeast Candida albicans (Sudbery et al., 2004; Mutlu et al., 2019). Highly related components of filamentation-signaling pathways are required for pathogenicity in C. albicans. The expression of the
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