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Title: Regulation of the E. coli Replicative Helicase DnaB by the Helicase Loader DnaC
Author: Atkinson, John David
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2007
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Abstract:
The helicase proteins directly ~esponsible for unwinding chromosomal DNA during DNA replication in bacteria, archaea and eukaryotes adopt a ring-shaped conformation for rapid displacement ofthe parental DNA duplex. As the DNA substrate is engulfed by the helicase during t~slocation, accessory proteins are required for placement ofthe helicase onto the DNA substrate either by breaking the ringed complex, thus allowing DNA to pass into the central channel, or by assembling the helicase around the DNA. In E. coli, the replicative helicase is a hexameric complex of six DnaB monomers, whilst the accessory loading partner is DnaC. Six DnaCmonomers associate with DnaB6 to assist in the loading ofthe helicase onto the DNA substrate. However, once present on the DNA, the presence ofDnaC on the DNA-bound helicase is thought to prevent the initiation of translocation. Only when DnaC has dissociated from DnaB6 will the helicase be permitted to commence unwinding ofthe duplex DNA. ,. Using in vitro enzymatic assays to identify the helicase activity ofDnaB on partial duplex DNA substrates, I have shown that when the concentration ofDnaC exceeds that ofDnaB, translocation and strand displacement by the helicase is not hindered when only one DNA strand is incorporated. When the helicase translocates over two DNA strands, however, movement is terminated via interaction with DnaC. More specifically, DnaB translocation is halted when DnaC is coupled with ATP, while interaction with ADP permits continued helicase movement. In vivo, the presence of DnaC within the DNA replication machinery complex could prove advantageous to the cell, as chromosomal duplication will only be permitted at bonefide replication forks. Keywords: DNA replication, helicase, DnaB, DnaC
Supervisor: Not available Sponsor: Not available
Qualification Name: University of Glasgow, 2007 Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.485809  DOI: Not available
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