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Abstract
SWM1 was originally identified for its role in the late steps of the sporulation process, being required for spore wall assembly. This protein, recently identified as one of the core subunits of the anaphase-promoting complex (APC) is also required to complete cell separation in vegetative cells during growth at high temperature. Mutants lacking SWM1 show a thermosensitive growth defect that is suppressed by osmotic support in the culture medium. At the restrictive temperature, swm1 mutants are unable to complete separation, forming chains of cells that remain associated and, with prolonged incubation times, the stability of the cell wall is compromised, resulting in cell lysis. This separation defect is due to a reduction in expression of CTS1 (the gene encoding chitinase) and a group of genes involved in cell separation (such as ENG1,SCW11, DSE1 and DSE2). Interestingly, these genes are specifically regulated by the transcription factor Ace2p, suggesting that Swm1p is required for normal expression of Ace2p-dependent genes during growth at high temperatures. Although no defect in Ace2p localization can be observed at 28 degrees C, this transcription factor is unable to enter the nucleus of the daughter cell during growth at 38 degrees C. Under these growth conditions, swm1 cells undergo a delay in exit from mitosis, as determined by analysis of Clb2p degradation and Cdc28p-Clb2p kinase assays, and this could be the reason for the cytoplasmic localization of Ace2p.
Highlights
Cell growth and morphogenesis is a complex process that is controlled by intricate signalling pathways and is tightly linked to the cell cycle. It has been extensively studied in Saccharomyces cerevisiae and involves several different processes that need to be perfectly coordinated in time and space to be successfully completed, such as specific programs of gene transcription (Cho et al, 1998; Spellman et al, 1998), selection of the new bud site (Chant, 1999), transport of new material to growth sites, or cell wall synthesis (Smits et al, 1999; Smits et al, 2001)
Results swm1 mutants have a thermosensitive growth defect We have previously reported that SWM1 expression is induced during sporulation and that its product is required for spore cell wall construction (Ufano et al, 1999)
These results indicated that Swm1p is required for the correct expression, during growth at high temperature, of the group of genes that are regulated by the transcription factor Ace2p, and that this effect is not due to a transcriptional defect of ACE2
Summary
Cell growth and morphogenesis is a complex process that is controlled by intricate signalling pathways and is tightly linked to the cell cycle It has been extensively studied in Saccharomyces cerevisiae (for a review, see Madden and Snyder, 1998) and involves several different processes that need to be perfectly coordinated in time and space to be successfully completed, such as specific programs of gene transcription (Cho et al, 1998; Spellman et al, 1998), selection of the new bud site (Chant, 1999), transport of new material to growth sites, or cell wall synthesis (Smits et al, 1999; Smits et al, 2001). A ubiquitin ligase, the anaphasepromoting complex (APC) or cyclosome, together with a specificity factor, ubiquitinates mitotic cyclins and targets them for degradation by the 26S proteasome
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