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. 2025 Sep 2;11(3):737-753.
doi: 10.3934/microbiol.2025031. eCollection 2025.

In Saccharomyces cerevisiae, the molecular chaperone proteins Ssb1 and Ssb2 upregulate ABC transporter genes, and their upregulation may play a role in the release of quorum-sensing molecules that induce cell growth arrest during the diauxic shift

Yoichi Yamada  1 , Mahiro Ota  2 , Atsuki Shiroma  2 , Takaki Matsuzawa  2
Affiliations

In Saccharomyces cerevisiae, the molecular chaperone proteins Ssb1 and Ssb2 upregulate ABC transporter genes, and their upregulation may play a role in the release of quorum-sensing molecules that induce cell growth arrest during the diauxic shift

Yoichi Yamada et al. AIMS Microbiol. .

Abstract

In Saccharomyces cerevisiae, the molecular chaperone proteins Ssb1 and Ssb2 (Ssb1/2) and the cochaperone ribosome-associated complex (Zuo1 and Ssz1) localize around the ribosome tunnel exit, assisting in the maturation of nascent polypeptides. Exogenous expression of the Zuo1 C-terminus or the Ssz1 N-terminus-but not Ssb1/2-independently activates the transcription factor Pdr1 (but not Pdr3), enhances the transcription of the ATP-binding cassette (ABC) transporter genes PDR5, SNQ2, and YOR1, and increases pleiotropic drug resistance. Furthermore, upregulation of ABC transporter genes by ZUO1 and SSZ1 leads to the release of quorum-sensing molecules, which cause cell growth arrest during diauxic shifts. In this study, we examined whether SSB1/2 are required for the expression of ABC transporter genes and the release of quorum-sensing molecules that lead to cell growth arrest during diauxic shifts. Our results show that Ssb1/2 increased the mRNA levels of PDR5, SNQ2, and YOR1 during the late logarithmic growth phase and increased resistance to cycloheximide and fluconazole, possibly via the same pathway as Zuo1 or Ssz1. Furthermore, Ssb1/2 induced PDR5 expression and resistance to cycloheximide and fluconazole, possibly via the same pathway as Pdr3 (but not Pdr1). In addition, it was suggested that Ssb1/2 are involved in the release of quorum-sensing molecules into the culture medium, which could signal cell growth arrest during diauxic shifts. This work provides useful knowledge regarding genetic interactions between the ribosome-associated molecular chaperone and cell growth arrest during diauxic shifts.

Keywords: ABC transporter; PDR5; SSB1; Saccharomyces cerevisiae; diauxic shift; molecular chaperone; quorum-sensing.

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Conflict of interest statement

Conflict of interest: The authors declare no conflict of interest.

Figures

Figure 1.
Figure 1.. SSB1/2 are responsible for cycloheximide and fluconazole resistance in S. cerevisiae. The resistance of the wild-type strain and its derivative mutant strains, ssb1∆ssb2∆, zuo1∆, ssb1∆, and ssz1∆, to fluconazole or cycloheximide was determined via a spot dilution assay.
Figure 2.
Figure 2.. mRNA levels of ABC transporters and their regulators in the wild-type and ssb1∆ssb2∆ strains during the early and late logarithmic growth phases. (A) The relative mRNA levels of PDR5, SNQ2, YOR1, PDR10, and PDR15 were determined in the wild-type and ssb1∆ssb2∆ strains at an OD600 of 0.6–0.8 via real-time RT-PCR. (B) Relative mRNA levels of PDR5, SNQ2, YOR1, PDR10, PDR15, PDR1, and PDR3 were determined in the wild-type and ssb1∆ssb2∆ strains at an OD600 of 1.2–1.6 via real-time RT-PCR. (C) Relative mRNA levels of PDR5, SNQ2, YOR1, PDR10, and PDR15 were determined in the wild-type at OD600 values of 0.6–0.8 and 1.2–1.6 via real-time RT-PCR. One asterisk (*) or two asterisks (**) indicate p values less than 0.05 or 0.01, respectively.
Figure 3.
Figure 3.. Analysis of epistatic interactions between SSB1/2 and PDR-related genes (ZUO1, SSZ1, PDR1, or PDR3) via real-time RT-PCR. Relative mRNA levels of PDR5, SNQ2, and YOR1 during the late logarithmic growth phase (OD600 of 1.6–1.9) were determined for each strain via real-time RT-PCR. The wild-type, ssb1∆ssb2∆, zuo1∆, ssz1∆, pdr1∆, pdr3∆, ssb1∆ssb2∆zuo1∆, ssb1∆ssb2∆ssz1∆, ssb1∆ssb2∆pdr1∆, and ssb1∆ssb2∆pdr3∆ strains transformed with an empty pRS313 plasmid are labeled wild-type pRS313, ssb1∆ssb2∆ pRS313, zuo1∆ pRS313, ssz1∆ pRS313, pdr1∆ pRS313, pdr3∆ pRS313, ssb1∆ssb2∆zuo1∆ pRS313, ssb1∆ssb2∆ssz1∆ pRS313, ssb1∆ssb2∆pdr1∆ pRS313, and ssb1∆ssb2∆pdr3∆ pRS313, respectively. The ssb1∆ssb2∆ mutant strain harboring pRS313–SSB1 is referred to as ssb1∆ssb2∆ pRS313–SSB1. Two asterisks (**) indicate p values less than 0.01.
Figure 4.
Figure 4.. Analysis of epistatic interactions between SSB1/2 and PDR-related genes (ZUO1, SSZ1, PDR1, or PDR3) via a spot dilution assay. (A) Resistance of the wild-type, ssb1∆ssb2∆, zuo1∆, ssz1∆, ssb1∆ssb2∆zuo1∆, and ssb1∆ssb2∆ssz1∆ strains with an empty pRS313 plasmid or pRS313–SSB1 to fluconazole or cycloheximide was determined via a spot dilution assay. (B) Resistance of the wild-type, ssb1∆ssb2∆, pdr1∆, pdr3∆, ssb1∆ssb2∆pdr1∆, and ssb1∆ssb2∆pdr3∆ strains with an empty pRS313 plasmid or pRS313–SSB1 to fluconazole or cycloheximide was determined via a spot dilution assay.
Figure 5.
Figure 5.. Addition of conditioned media from the wild-type strain alters the growth of ssb1∆ssb2∆ mutant cells during the diauxic shift. (A) The black circles with solid lines represent the growth curve of the wild-type strain, and the grey squares with solid lines represent the growth curve of the ssb1∆ssb2∆ mutant strain. The black circles with dotted lines represent the growth curve of the wild-type strain, in which the culture media were replaced with conditioned media from the ssb1∆ssb2∆ mutant strain at 21 h after the start of incubation. The grey squares with dotted lines represent the growth curve of the ssb1∆ssb2∆ mutant strain, in which the culture media were replaced with conditioned media from the wild-type cells at 21 h after the start of incubation. (B) The black circles with solid lines represent the growth curve of the wild-type strain, in which the culture media were replaced with conditioned media from the wild-type strain at 21 h after the start of incubation. The grey squares with solid lines represent the growth curve of the ssb1∆ssb2∆ mutant strain, in which the culture media were replaced with conditioned media from the ssb1∆ssb2∆ mutant cells at 21 h after the start of incubation.
Figure 6.
Figure 6.. Network model mediating quorum-sensing molecule release via Ssb1/2, Zuo1, and Ssz1. In this model, Ssb1/2, Zuo1, and Ssz1 assist in the proper folding of the transcription factors Pdr1 and Pdr3, thereby enhancing the expression of the ABC transporter genes PDR5, SNQ2, and Yor1. The ABC transporters Pdr5 and Snq2 mediate the export of quorum-sensing molecules into the extracellular space.
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References

    1. DeRisi JL, Iyer VR, Brown PO. Exploring the metabolic and genetic control of gene expression on a genomic scale. Science. 1997;278:680–686. doi: 10.1126/science.278.5338.680. - DOI - PubMed
    1. Ashe MP, De Long SK, Sachs AB. Glucose depletion rapidly inhibits translation initiation in yeast. Mol Biol Cell. 2000;11:833–848. doi: 10.1091/mbc.11.3.833. - DOI - PMC - PubMed
    1. Stahl G, Salem SN, Chen L, et al. Translational accuracy during exponential, postdiauxic, and stationary growth phases in Saccharomyces cerevisiae. Eukaryot Cell. 2004;3:331–338. doi: 10.1128/ec.3.2.331-338.2004. - DOI - PMC - PubMed
    1. Willmund F, del Alamo M, Pechmann S, et al. The cotranslational function of ribosome-associated Hsp70 in eukaryotic protein homeostasis. Cell. 2013;152:196–209. doi: 10.1016/j.cell.2012.12.001. - DOI - PMC - PubMed
    1. Döring K, Ahmed N, Riemer T, et al. Profiling Ssb-Nascent Chain Interactions Reveals Principles of Hsp70-Assisted Folding. Cell. 2017;170:298–311. - PMC - PubMed

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