Use this URL to cite or link to this record in EThOS:
Title: Initiation of asymmetric rolling-circle plasmid replication by RepD studied using magnetic tweezers
Author: Toleikis, A.
ISNI:       0000 0004 7964 756X
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2016
Availability of Full Text:
Access from EThOS:
Full text unavailable from EThOS. Please try the link below.
Access from Institution:
Bacterial drug resistance is often carried by circular DNA plasmids. As plasmids are copied separately from the bacterial genomic DNA, the copies can be passed to other bacteria in the colony spreading the antibiotic resistance. This PhD thesis describes studies of the replication machinery, used by the Staphylococcus aureus chloramphenicol-resistance plasmid pC221. The plasmid is duplicated by a process called asymmetric rolling circle replication, in which the two DNA strands are copied asynchronously. It is not fully understood how the replication process is regulated but the initiation requires a plasmid-encoded protein, in this case RepD. This initiator nicks the parent, supercoiled plasmid at the double-stranded origin of replication (here, oriD) and reveals a short length of single-stranded DNA, which allows a helicase and DNA polymerase to bind. These together unwind and copy the leading strand. Here, custom-built magnetic tweezers were used to control the extent of supercoiling and monitor the RepD nicking reaction of single molecules of linear DNA. I found that the nicking reaction is exquisitely sensitive to DNA supercoiling, which means replication cannot start if the plasmid is relaxed by damage or if replication is already in process. DNA supercoiling therefore acts as a mechanical signal to control initiation and as safety-catch to prevent re-initiation at the newly synthesized oriD site until the new, complete, circular daughter plasmid has been created and supercoiled. The role of DNA supercoiling therefore is not merely compaction but also an important regulator of protein-DNA interactions in DNA replication.
Supervisor: Molloy, J. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available