This study concerns the analysis of elements involved in the control over entry into mitosis in the fission yeast, <i>Schizosaccharomyces pombe</i>. The initial aim was to characterise the role of the <i>win1</i> gene in this control system. The <i>win1</i>.1 mutation shows a strong interaction with <i>wee1</i> and <i>cdc25</i>, genes which had previously been shown to play an important role in the control over entry into mitosis, probably acting through the <i>cdc2</i> protein kinase. The strategy for the cloning of <i>win1</i> was to isolate sequences capable of suppressing the temperature sensitive cdc phenotype arising from the combination of <i>win1.1</i> with <i>wee1.50</i> and <i>cdc25.22</i>. Following the extensive screening of gene libraries, it proved impossible to isolate <i>win1</i> using this approach, although five new genes were isolated as multicopy suppressors of this phenotype. None of these sequences correspond to any known mitotic control gene, and therefore identify new genes that affect the control of entry into mitosis. These were named <i>wis</i> (<i>wi</i>n <i>s</i>uppressing) 1 to 5. A molecular analysis was undertaken on the pwis plasmids, and the phenotypes of various cell cycle mutant strains containing the pwis plasmids were also examined. <i>wis1</i><SUP>+</SUP> was found to be capable of reducing the cell length at division in a dosage dependent manner, suggesting that <i>wis1</i> is involved in a rate limiting step controlling entry into mitosis. A null allele of <i>wis1</i> was constructed and found to result in large cells which have poor viability upon entry into stationary phase. DNA sequence analysis of <i>wis1</i> predicts a 605 amino acid gene product with a strong homology to serine/threonine protein kinases. Strains lacking in <i>wis1</i> function are still sensitive to levels of <i>wee1</i> and <i>cdc25</i> expression, suggesting that <i>wis1</i> acts upstream of these control elements. The interaction of <i>win1.1</i> with other cell cycle mutants was studied and the <i>win1</i> locus mapped. The cloning of the closely linked gene <i>tps19</i> could provide an alternative strategy for the isolation of <i>win1</i>. Both <i>win1.1</i> and a <i>wis1</i><SUP>-</SUP> allele were found to be capable of suppressing the hypersporulation phenotype of <i>pat1</i><SUP>ts</SUP> mutations, suggesting that the <i>win1</i> and <i>wis1</i> gene products may play a role in the regulation both of mitosis and meiosis.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:663463 |
| Date | January 1990 |
| Creators | Warbrick, Emma |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13203 |
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