Abstract
The yeast Saccharomyces cerevisiae normally selects bud sites (and hence axes of cell polarization) in one of two distinct patterns, the axial pattern of haploid cells and the bipolar pattern of diploid cells. Although many of the proteins involved in bud-site selection are known, it is likely that others remain to be identified. Confirming a previous report (Ni and Snyder, 2001, Mol. Biol. Cell 12, 2147–2170), we found that diploids homozygous for deletions of IST3/SNU17 or BUD13 do not show normal bipolar budding. However, these abnormalities do not reflect defects in the apparatus of bipolar budding. Instead, the absence of Ist3 or Bud13 results in a specific defect in the splicing of the MAT a 1 pre-mRNA, which encodes a repressor that normally blocks expression of haploid-specific genes in diploid cells. When Mata1 protein is lacking, Axl1, a haploid-specific protein critical for the choice between axial and bipolar budding, is expressed ectopically in diploid cells and disrupts bipolar budding. The involvement of Ist3 and Bud13 in pre-mRNA splicing is by now well known, but the degree of specificity shown here for MAT a 1 pre-mRNA, which has no obvious basis in the pre-mRNA structure, is rather surprising in view of current models for the functions of these proteins. Moreover, we found that deletion of PML1, whose product is thought to function together with Ist3 and Bud13 in a three-protein retention-and-splicing (RES) complex, had no detectable effect on the splicing in vivo of either MAT a 1 or four other pre-mRNAs.
Highlights
A central feature of cell polarization is selection of the appropriate axis
As reported by Ni and Snyder [21], we found that deletion of IST3 or BUD13 had no detectable effect on the axial budding pattern of haploid cells but profoundly affected the bipolar budding pattern of homozygous diploid mutants
[14] See text See text Segregant from STY216 Segregant from STY229 This studyc This studyc See text This studyd Segregant from STY450 This studyc This studye See text This studyf See text Segregant from STY2416STY604 This studyg This studyh STY6046STY605 This studyi See text This studyj This studyj aAll strains are congenic to YEF473 except as indicated. bThe mutations were generated by the polymerase chain reaction (PCR) method [34,35]
Summary
A central feature of cell polarization is selection of the appropriate axis. In the yeast Saccharomyces cerevisiae, this axis is defined by selection of the bud site, which occurs in one of two distinct patterns, depending on the cell type [1,2]. The bipolar pattern depends on persistent cortical markers at both the birth-scar-proximal and distal cell poles that involve the proteins Bud, Bud, Rax, and Rax2 [2,10,11,12,13,14,15,16]. In both budding patterns, the positions of the cortical markers appear to be transmitted through a signal module based on the Ras-like protein Rsr1/Bud to the Rho-like protein Cdc, whose localized activation triggers the polarization of the cytoskeletal and secretary systems [10,17,18]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
