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Title: New elements of the mitotic control in Schizosaccharomyces pombe
Author: Warbrick, Emma
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1990
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This study concerns the analysis of elements involved in the control over entry into mitosis in the fission yeast, Schizosaccharomyces pombe. The initial aim was to characterise the role of the win1 gene in this control system. The win1.1 mutation shows a strong interaction with wee1 and cdc25, genes which had previously been shown to play an important role in the control over entry into mitosis, probably acting through the cdc2 protein kinase. The strategy for the cloning of win1 was to isolate sequences capable of suppressing the temperature sensitive cdc phenotype arising from the combination of win1.1 with wee1.50 and cdc25.22. Following the extensive screening of gene libraries, it proved impossible to isolate win1 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 wis (win suppressing) 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. wis1+ was found to be capable of reducing the cell length at division in a dosage dependent manner, suggesting that wis1 is involved in a rate limiting step controlling entry into mitosis. A null allele of wis1 was constructed and found to result in large cells which have poor viability upon entry into stationary phase. DNA sequence analysis of wis1 predicts a 605 amino acid gene product with a strong homology to serine/threonine protein kinases. Strains lacking in wis1 function are still sensitive to levels of wee1 and cdc25 expression, suggesting that wis1 acts upstream of these control elements. The interaction of win1.1 with other cell cycle mutants was studied and the win1 locus mapped. The cloning of the closely linked gene tps19 could provide an alternative strategy for the isolation of win1. Both win1.1 and a wis1- allele were found to be capable of suppressing the hypersporulation phenotype of pat1ts mutations, suggesting that the win1 and wis1 gene products may play a role in the regulation both of mitosis and meiosis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available