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Kluyveromyces lactis SSO1 and SEB1 genes are functional in Saccharomyces cerevisiae and enhance production of secreted proteins when overexpressed

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The SEB1/SBH1 and the SSO genes encode components of the protein secretory machinery functioning at the opposite ends, ER translocation and exocytosis, respectively, of the secretory pathway of Saccharomyces cerevisiae. Overexpression of these genes can rescue temperature-sensitive (ts) growth defect of many sec mutants impaired in protein secretion. Their overexpression in wild-type yeast enhances production of secreted proteins in S. cerevisiae, which suggests that may be rate-limiting factors in this process.


Kluyveromyces lactis homologs of S. cerevisiae SEB and SSO genes were isolated by multicopy suppression of Saccharomyces mutations [1]. KlSSO1 and KlSEB1 are up to 70 % identical with the S. cerevisiae homologs at the amino acid level and can functionally replace them. These single copy genes were able to complement the ts growth defect of sso2-1 and seb1 Δ seb2 Δ sem1 Δ strains, respectively. In addition, KlSSO1 multicopy suppressed both sporulation defects of S. cerevisiae mutants sso1 Δ/sso1 Δ or mso1 Δ/mso1 Δ and ts growth defect of exocyst mutant sec15-1. Furthermore, KlSSO1 and KlSEB1 enhanced production of a secreted protein (Fig.1) similarly to SSO and SEB1 genes of S. cerevisiae [2, 3] when overexpressed.

Figure 1

Increased production of secreted α-amylase by overexpression of KlSSO1 (▲) and KlSEB1 (■) in comparison to the control strain carrying empty vector (). The cell growth is presented with open symbols.


The single copy genes KlSSO1 and KlSEB1 are both structurally and functionally conserved in evolution with their duplicated S. cerevisiae homologs.


  1. 1.

    Toikkanen JH, Sundqvist L, Keränen S: Kluyveromyces lactis SSO1 and SEB1 genes are functional in Saccharomyces cerevisiae and enhance production of secreted proteins when overexpressed. Yeast. 2004, 21: 1045-1055. 10.1002/yea.1151.

  2. 2.

    Ruohonen L, Toikkanen J, Tieaho V, Outola M, Söderlund H, Keränen S: Enhancement of protein secretion in Saccharomycescerevisiae by overproduction of Sso protein, a late-acting component of the secretory machinery. Yeast. 1997, 13: 337-351. 10.1002/(SICI)1097-0061(19970330)13:4<337::AID-YEA98>3.0.CO;2-K.

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    Toikkanen JH, Miller KJ, Söderlund H, Jäntti J, Keränen S: The β subunit of the Sec61p endoplasmic reticulum translocon interacts with the exocyst complex in Saccharomyces cerevisiae. J Biol Chem. 2003, 278: 20946-20953. 10.1074/jbc.M213111200.

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Correspondence to Jaana H Toikkanen.

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  • Saccharomyces Cerevisiae
  • Lactis
  • Saccharomyces
  • Secrete Protein
  • Secretory Pathway