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.

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Journal Article

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Yamada Y, Ota M, Shiroma A, Matsuzawa T

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