The role of Rho5 in Kluyveromyces lactis

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Title: The role of Rho5 in Kluyveromyces lactis
Authors: Musielak, Marius
Thesis advisor: Prof. Dr. Jürgen J. Heinisch
Thesis referee: Prof. Dr. Achim Paululat
Abstract: Small GTPases are important signalling hubs which coordinate extra and intracellular cues with a proper adaptive response, and thereby ensure the survival of cells and organisms. In the model yeast S. cerevisiae the small GTPase Rho5, a homologue of the well studied human Rac1, mediates the response to both low and high medium osmolarity (CWI- and HOG-pathway, respectively), oxidative stress and nutrient availability. Here the roles of its homologue KlRho5, from the diary yeast Kluyveromyces lactis, in these and other signalling pathways were assessed. First, in silico analyses including sequence alignments were employed to identify the homologues of RHO5 and the genes encoding the subunits of its dimeric GEF, DCK1 and LMO1, in the K. lactis genome. Upon cloning and heterologous expression, KlRHO5 complemented the phenotypes of a Scrho5 deletion. Deletion mutants in either of the three genes altered their sensitivities to oxidative and cell wall stress conditions. Moreover, KlRho5 and its bipartite GEF KlDck1/KlLmo1 showed similar intracellular distributions as their S. cerevisiae counterparts. Thus both oxidative stress and glucose starvation caused a rapid translocation of the proteins to the mitochondria. A novel function for KlRho5 was discovered in the regulation of cytokinesis, as deletion mutants displayed protruding bud scars, aberrant primary septa and a thickened cell wall. KlCdc42, another protein of the same small GTPase subfamily, participates in yeast bud site selection and was found to largely complement the morphological defects of Klrho5 deletions, indicating overlapping functions. KlCd42 also shares the rapid translocation to mitochondria under oxidative stress. Thus, KlRho5 was found to regulate oxidative stress response, adaption to glucose starvation and cytokinesis. Whereas the first two functions are apparently shared with its homologue in S. cerevisiae, the latter seems to be specific for K. lactis
Subject Keywords: Kluyveromyces lactis; Rho5
Issue Date: 31-Jan-2023
License name: Attribution 3.0 Germany
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Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB05 - E-Dissertationen

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