Sponsor
Portland State University. Department of Biology
First Advisor
Justin Courcelle
Term of Graduation
Fall 2024
Date of Publication
12-9-2024
Document Type
Thesis
Degree Name
Master of Science (M.S.) in Biology
Department
Biology
Language
English
Subjects
DNA replication, DNA topoisomerases
Physical Description
1 online resource (v, 48 pages)
Abstract
Accurate replication of the genome is essential to maintain cellular life. Completing DNA replication on the chromosome is central to this task and involves several enzymes, including RecBCD, RecG and SbcCD-ExoI, which process, join, and resolve the two convergent replication forks. This event is certain to generate a number of structural complexities involving supercoiling, tangles and knots as the two DNA replication forks converge which must be resolved to maintain the integrity of the genome. Structural knots and tangles generated during DNA replication, transcription and segregation are typically resolved by DNA topoisomerases. E. coli encodes four DNA topoisomerases--two type I (Topo I and Topo III) and two type II (Topo IV and DNA gyrase). Here, we used mini-chromosomes that require replisomes to converge to identify which topoisomerases participate in processing substrates during completion. I show that mutants lacking Topo I, but not Topo III, are impaired in their ability to maintain substrates containing convergent replication forks. Additionally Topo IV, but not gyrase, contributes to the completion step on plasmids. I then confirmed these results on the E. coli chromosome where distinct phenotypes were observed in each case. Impaired Topo I function led to amplifications where forks converge, whereas loss of Topo IV activity resulted in extensive degradation and loss of this chromosome region. I discuss models in which Topo I plays a general role in maintaining supercoiling to allow replisomes to converge, whereas Topo IV plays a more specific role and is required to allow the nascent strand ends of convergent forks to be joined.
Rights
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Persistent Identifier
https://archives.pdx.edu/ds/psu/43008
Recommended Citation
Mokhtari, Parisa, "The Role of DNA Topoisomerases in the Completion of DNA Replication" (2024). Dissertations and Theses. Paper 6757.