A Genomic Study of the Bipolar Bud Site Selection Pattern inSaccharomyces cerevisiae

Abstract

A genome-wide screen of 4168 homozygous diploid yeast deletion strains has been performed to identify nonessential genes that participate in the bipolar budding pattern. By examining bud scar patterns representing the sites of previous cell divisions, 127 mutants representing three different phenotypes were found: unipolar, axial-like, and random. From this screen, 11 functional classes of known genes were identified, including those involved in actin-cytoskeleton organization, general bud site selection, cell polarity, vesicular transport, cell wall synthesis, protein modification, transcription, nuclear function, translation, and other functions. Four characterized genes that were not known previously to participate in bud site selection were also found to be important for the haploid axial budding pattern. In addition to known genes, we found 22 novel genes (20 are designated BUD13-BUD32) important for bud site selection. Deletion of one resulted in unipolar budding exclusively from the proximal pole, suggesting that this gene plays an important role in diploid distal budding. Mutations in 20 other novel BUD genes produced a random budding phenotype and one produced an axial-like budding defect. Several of the novel Bud proteins were fused to green fluorescence protein; two proteins were found to localize to sites of polarized cell growth (i.e., the bud tip in small budded cells and the neck in cells undergoing cytokinesis), similar to that postulated for the bipolar signals and proteins that target cell division site tags to their proper location in the cell. Four others localized to the nucleus, suggesting that they play a role in gene expression. The bipolar distal marker Bud8 was localized in a number of mutants; many showed an altered Bud8-green fluorescence protein localization pattern. Through the genome-wide identification and analysis of different mutants involved in bipolar bud site selection, an integrated pathway for this process is presented in which proximal and distal bud site selection tags are synthesized and localized at their appropriate poles, thereby directing growth at those sites. Genome-wide screens of defined collections of mutants hold significant promise for dissecting many biological processes in yeast.

The Cdc42 Effectors Ste20, Cla4, and Skm1 Down-Regulate the Expression of Genes Involved in Sterol Uptake by a Mitogen-activated Protein Kinase-independent Pathway

“…Previously, we could show that Ste20 binds to Erg4, Cbr1, and Ncp1, which all catalyze important steps in sterol biosynthesis (Tiedje et al, 2007). Interestingly, these proteins are also involved in bud site selection, apical bud growth, mating, filamentous growth, and exit from mitosis (Ni and Snyder, 2001;Keniry et al, 2004;Tiedje et al, 2007). These observations highlight the importance of sterol synthesis for cell polarization.…”

“…Very little is known about Skm1, and no clear function has been attributed to this PAK (Martín et al, 1997). Interestingly, Ste20 and Cla4 interact with Erg4, Cbr1 and Ncp1, which are all involved in sterol biosynthesis, and the deletion of the corresponding genes results in various polarity defects, suggesting that sterol biosynThis article was published online ahead of print in MBC in Press (http://www.molbiolcell.org/cgi/doi/10.1091/mbc.E09 -01-0034) on September 30, 2009. thesis is crucial for cell polarization (Ni and Snyder, 2001;Tiedje et al, 2007).…”

“…© 2009 by The American Society for Cell Biology thesis is crucial for cell polarization (Ni and Snyder, 2001;Tiedje et al, 2007). Many aspects of sterol homeostasis are conserved between yeast and human, and ergosterol, the predominant sterol of yeast, is structurally and functionally related to sterols of higher eukaryotes (Sturley, 2000).…”

Cell Polarity in Saccharomyces cerevisiae Depends on Proper Localization of the Bud9 Landmark Protein by the EKC/KEOPS Complex

“…A genome-wide screening of homozygous deletion mutants identified 127 mutants representing three different bud-site phenotypes: unipolar, axial-like, and random (Ni and Snyder 2001). Among them, 112 mutants displayed strong or weak random budding phenotypes.…”

“…Among them, 112 mutants displayed strong or weak random budding phenotypes. The homozygous deletion mutant of the gene BUD32 displayed a random budding pattern (Ni and Snyder 2001). BUD32 was originally found as a gene encoding an atypical protein kinase that belongs to the piD261 family of atypical Ser/Thr protein kinases found in virtually all eukaryotic and archaeal organisms (Stocchetto et al 1997).…”