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Research Support, N.I.H., Extramural
- Phenotypes Associated with Saccharomyces cerevisiae Hug1 Protein, a Putative Negative Regulator of dNTP Levels, Reveal Similarities and Differences with Sequence-Related Dif1
- Eunmi Kim# , Wolfram Siede
- J. Microbiol. 2011;49(1):78-85. Published online March 3, 2011
- DOI: https://doi.org/10.1007/s12275-011-0200-8
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- 4 Scopus
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Abstract
- Saccharomyces cerevisiae Hug1 is a small protein of unknown function that is highly inducible following replication stress and DNA damage. Its deletion suppresses the lethality of deletion of checkpoint kinase Mec1. Although DNA damage responses were largely normal in the HUG1 deletion mutant, we found enhanced resistance towards heat in logarithmic phase. In response to simultaneous carbon and replication stress, overall growth delay and less pseudohyphal filament formation were evident. These novel phenotypes are shared with deletion mutants of the negative regulators of ribonucleotide reductase, Dif1 and Sml1. Microarray analysis showed the influence of Hug1 on the expression of a large number of transcripts, including stress-related transcripts. Elevated dNTP levels in hug1Δ cells may result in a stress response reflected by the observed phenotypes and transcript profiles. However, in contrast to a deletion of structurally related Dif1, Rnr2-Rnr4 subcellular localization is not grossly altered in a Hug1 deletion mutant. Thus, although Hug1 appears to be derived from the Rnr2-Rnr4 binding region of Dif1, its mechanism of action must be independent of determining the localization of Rnr2-Rnr4.
Research Support, Non-U.S. Gov'ts
- Phosphorylation-Dependent Septin Interaction of Bni5 is Important for Cytokinesis
- Sung Chang Nam , Hyeran Sung , Seung Hye Kang , Jin Young Joo , Soo Jae Lee , Yeon Bok Chung , Chong-Kil Lee , Sukgil Song
- J. Microbiol. 2007;45(3):227-233.
- DOI: https://doi.org/2538 [pii]
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Abstract
- In budding yeast, septin plays as a scaffold to recruits protein components and regulates crucial cellular events including bud site selection, bud morphogenesis, Cdc28 activation pathway, and cytokinesis. Phosphorylation of Bni5 isolated as a suppressor for septin defect is essential to Swe1-dependent regulation of bud morphogenesis and mitotic entry. The mechanism by which Bni5 regulates normal septin function is not completely understood. Here, we provide evidence that Bni5 phosphorylation is important for interaction with septin component Cdc11 and for timely delocalization from septin filament at late mitosis. Phosphorylation-deficient bni5-4A was synthetically lethal with hof1Δ. bni5-4A cells had defective structure of septin ring and connected cell morphology, indicative of defects in cytokinesis. Two-hybrid analysis revealed that bni5-4A has a defect in direct interaction with Cdc11 and Cdc12. GFP-tagged bni5-4A was normally localized at mother-bud neck of budded cells before middle of mitosis. In contrast, at large-budded telophase cells, bni5-4A-GFP was defective in localization and disappeared from the neck approximately 2 min earlier than that of wild type, as evidenced by time-lapse analysis. Therefore, earlier delocalization of bni5-4A from septin filament is consistent with phosphorylation-dependent interaction with the septin component. These results suggest that timely delocalization of Bni5 by phosphorylation is important for septin function and regulation of cytokinesis.
- Requirement of Bni5 Phosphorylation for Bud Morphogenesis in Saccharomyces cerevisiae
- Sung Chang Nam , Hyeran Sung , Yeon Bok Chung , Chong-Kil Lee , Dong Hun Lee , Sukgil Song
- J. Microbiol. 2007;45(1):34-40.
- DOI: https://doi.org/2494 [pii]
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Abstract
- In budding yeast, G2/M transition is tightly correlated with bud morphogenesis regulated by Swe1 and septin that plays as a scaffold to recruits protein components. BNI5 isolated as a suppressor for septin defect is implicated in septin organization and cytokinesis. The mechanism by which Bni5 regulates normal septin function is not completely understood. Here, we show that Bni5 phosphorylation is required for mitotic entry regulated by Swe1 pathway. Bni5 modification was evident from late mitosis to G1 phase, and CIP treatment in vitro of affinity-purified Bni5 removed the modification, indicative of phosphorylation on Bni5. The phosphorylation-deficient mutant of BNI5 (bni5-4A) was defective in both growth at semi-restrictive temperature and suppression of septin defect. Loss of Bni5 phosphorylation resulted in abnormal bud morphology and cell cycle delay at G2 phase, as evidenced by the formation of elongated cells with multinuclei. However, deletion of Swe1 completely eliminated the elongated-bud phenotypes of both bni5 deletion and bni5-4A mutants. These results suggest that the bud morphogenesis and mitotic entry are positively regulated by phosphorylation-dependent function of Bni5 which is under the control of Swe1 morphogenesis pathway.
- A New Function of Skp1 in the Mitotic Exit of Budding Yeast Saccharomyces cerevisiae
- Namil Kim , Hayoung Yoon , Eunhwa Lee , Kiwon Song
- J. Microbiol. 2006;44(6):641-648.
- DOI: https://doi.org/2463 [pii]
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Abstract
- We previously reported that Skp1, a component of the Skp1-Cullin-F-box protein (SCF) complex essential for the timely degradation of cell cycle proteins by ubiquitination, physically interacts with Bfa1, which is a key negative regulator of the mitotic exit network (MEN) in response to diverse checkpoint-activating stresses in budding yeast. In this study, we initially investigated whether the interaction of Skp1 and Bfa1 is involved in the regulation of the Bfa1 protein level during the cell cycle, especially by mediating its degradation. However, the profile of the Bfa1 protein did not change during the cell cycle in skp1-11, which is a SKP1 mutant allele in which the function of Skp1 as a part of SCF is completely impaired, thus indicating that Skp1 does not affect the degradation of Bfa1. On the other hand, we found that the skp1-12 mutant allele, previously reported to block G2-M transition, showed defects in mitotic exit and cytokinesis. The skp1-12 mutant allele <br><br>also revealed a specific genetic interaction with Δbfa1. Bfa1 interacted with Skp1 via its 184 C-terminal residues (Bfa1-D8) that are responsible for its function in mitotic exit. In addition, the interaction between Bfa1 and the Skp1-12 mutant protein was stronger than that of Bfa1 and the wild type Skp1. We suggest a novel function of Skp1 in mitotic exit and cytokinesis, independent of its function as a part of the SCF complex. The interaction of Skp1 and Bfa1 may contribute to the function of Skp1 in the mitotic exit.
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