Taheri N, Koehler T, Braus GH, Moesch HU

Institute of Microbiology and Genetics, Georg August University, Grisebachstrasse 8, D-37077 Goettingen, Germany.

Diploid strains of the budding yeast Saccharomyces cerevisiae change the pattern of cell division from bipolar to unipolar when switching growth from the unicellular yeast form (YF) to filamentous, pseudohyphal (PH) cells in response to nitrogen starvation. The functions of two transmembrane proteins, Bud8p and Bud9p, in regulating YF and PH cell polarity were investigated. Bud8p is highly concentrated at the distal pole of both YF and PH cells, where it directs initiation of cell division. Asymmetric localization of Bud8p is independent of the Rsr1p/Bud1p GTPase. rsr1/bud1 mutations are epistatic to bud8 mutations, placing Rsr1p/Bud1p downstream of Bud8p. In YF cells, Bud9p is also localized at the distal pole, yet deletion of BUD9 favours distal bud initiation. In PH cells, nutritional starvation for nitrogen efficiently prevents distal localization of Bud9p. Because Bud8p and Bud9p proteins associate in vivo, we propose Bud8p as a landmark for bud initiation at the distal cell pole, where Bud9p acts as inhibitor. In response to nitrogen starvation, asymmetric localization of Bud9p is averted, favouring Bud8p-mediated cell division at the distal pole.

Mesh Terms:
Cell Polarity, Fluorescent Antibody Technique, Indirect, Fungal Proteins, Genotype, Green Fluorescent Proteins, Luminescent Proteins, Membrane Glycoproteins, Models, Biological, Plasmids, Recombinant Fusion Proteins, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, rab GTP-Binding Proteins

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