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Dissertation
The regulation of meiotic S phase in Saccharomyces cerevisiae
Doctor of Philosophy (Ph.D.), Drexel University
May 2005
DOI:
https://doi.org/10.17918/00009288
Abstract
Protein phosphatase 2A is a heterotrimeric serine/threonine phosphatase comprised of two regulatory subunits and a catalytic subunit. We have found that the gene encoding one of two B regulatory subunits, CDC55, is required for meiotic progression. Mutant cells lacking CDC55 are capable of inducing the early meiotic genes, IME1 and IME2, but are defective in the expression of the middle sporulation gene, NDT80. Furthermore, we find that cdc55 cells are capable of completing intragenic recombination, but are defective in premeiotic DNA replication, intergenic recombination, harbor spindle pole body duplication and microtubule elongation defects, and are unable to sporulate. We are unable to bypass defects caused by the loss of CDC55 by deletion of genes that act at the pachytene checkpoint that monitors recombination. However, deletion of the DNA damage checkpoint gene, RAD9, allows for the partial suppression of premeiotic DNA replication and sporulation defects. Additionally, we find that deletion of CDC55 and CLB5, which encodes for the major S phase B-type cyclin, is synthetically lethal. Taken together, these data suggest that CDC55 is required at premeiotic S phase. In parallel studies, we have discovered two mutants that are able to complete several rounds of premeiotic S phase and form asci containing more than four spores, called multi-spores. Deletion of the tyrosine kinase and CDK inhibitor, SWE1, or expression of the constitutively active allele, CDC28AF, allows for the re-initiation of replication within one meiotic cycle. Multi-spores contain even and odd number of viable spores, which exhibit Mendelian segregation and are capable of homologous recombination. The Rad9p- and Rad17p-dependent checkpoints are not required for multi-spore formation; deletion of the S phase cyclin, CLB6, or the CDK inhibitor, SIC1, does not affect multi-sporulation. Interestingly, there is a requirement for the premeiotic S phase proteins, Clb5p and Cdc55p, as well as the recombination proteins, Spo11p and Rec102p, for re-replication. The fact that cdc55, swe1, and CDC28AF mutants are replication-competent during mitotic S phase but exhibit defects during premeiotic S phase suggests that mitotic and premeiotic DNA replication is regulated differently during these processes.
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Details
- Title
- The regulation of meiotic S phase in Saccharomyces cerevisiae
- Creators
- Lyndi Michelle Rice
- Contributors
- Joseph T. Nickels (Advisor) - Drexel University, Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Doctor of Philosophy (Ph.D.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- ix, 154 pages
- Resource Type
- Dissertation
- Language
- English
- Academic Unit
- Biochemistry and Molecular Biology; College of Medicine; Drexel University
- Other Identifier
- 991021889094504721