Defense Date

1-7-2009

Graduation Date

Spring 2009

Availability

Immediate Access

Submission Type

dissertation

Degree Name

PhD

Department

Biological Sciences

Committee Chair

Joseph McCormick

Committee Member

Peter Castric

Committee Member

Nancy Trun

Committee Member

Patrick Viollier

Keywords

DNA segregation, cell division, DNA condensation

Abstract

DNA segregation and condensation must occur accurately during cell division to ensure the survival of daughter cells. Most prokaryotes have a single, circular genome, which is simultaneously replicated, segregated and condensed during cell division. Streptomyces coelicolor is a sporulating, filamentous bacterium with a large, linear genome. Syncytial aerial hyphae contain numerous copies of the genome, which must be synchronously segregated into prespore compartments while up to 100 septa form. The proteins that control and accomplish this complicated process are of interest. Genetic analysis revealed that S. coelicolor can survive without three DNA segregation proteins, SMC, FtsK and ParB, which normally result in synthetic lethal phenotypes in unicellular bacteria. A ∆smc ∆ftsK ∆parB triple mutant was still able to segregate genetic material to 90% of its spores, but exhibited a fourfold decrease in viability when compared to wild type.

For S. coelicolor, there must be considerable redundancy in genome segregation to overcome the loss of these genes. Furthermore, the large genome of S. coelicolor has to be properly condensed in order for it to fit inside a spore which is 1 μm in length. Genetic analysis of scpA and scpB, the gene products are thought to be involved in DNA condensation by interaction with SMC, revealed that neither were required for viability, but produced spores with a bilobed DNA architecture, unlike wild type or ∆smc mutant spores. It was concluded that this morphological phenotype was not the result of an interaction of the scpAB with smc, as the smc mutant did not present this phenotype. This bilobed nature of the scp mutants prompted the investigation of spore ploidy. Using several different but complementary methods, evidence was obtained suggesting that S. coelicolor spores and that of other species are diploid. A specific and dynamic movement of the origin of replication was discovered very late in spore development and a novel gene, parA2, was found to directly or indirectly play a role in this process. Together, these data reveal new information in order to better understand how linear chromosomal DNA is segregated, condensed and localized in this sporulating bacterium.

Format

PDF

Language

English

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