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Quaternary Polymorphism in Helicases and the DnaB.DnaC Complex

Published online by Cambridge University Press:  02 July 2020

L.E. Donate ,
M. Bárcena ,
O. Llorca ,
N. Dixon  and
J.M. Carazo
L.E. Donate
Affiliation:
Centro Nacional de Biotecnologia. BioComputing Unit.28049Mdrid.Spain
M. Bárcena
Affiliation:
Centro Nacional de Biotecnologia. BioComputing Unit.28049Mdrid.Spain
O. Llorca
Affiliation:
Centro Nacional de Biotecnologia. BioComputing Unit.28049Mdrid.Spain
N. Dixon
Affiliation:
Centre for Molecular Structure and Function. Australian National University.CanberraACT0200.
J.M. Carazo
Affiliation:
Centro Nacional de Biotecnologia. BioComputing Unit.28049Mdrid.Spain
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Extract

Strand separation in double stranded DNA is achieved in vivo by a class of enzymes called helicases in a process fuelled by hydrolysis of nucleoside triphosphates. DnaB is the major replicative helicase in E.coli. For chromosomal replication to initiate, DnaB needs to interact with a partner protein, namely DnaC, which after properly loading DnaB onto the DNA template at the origin of replication is subsequently released from the complex. DnaB turns to be functionally active as a helicase only after DnaC has been released from the complex. The native DnaB is a homohexamer of molecular weight 318 kD. In the presence of ATP and Mg2+, the hexameric DnaB has been shown to form a complex with six molecules of DnaC (total molecular weight of the complex: 480 kD).

The reconstructed 3D volume of the DnaB hexamer obtained from frozen-hydrated specimens showed the DnaB oligomer as a particle possessing three-fold rather than six-fold symmetry, despite DnaB being made up by six identical subunits.

Type
Electron Cryomicroscopy of Macromolecules
Information
Microscopy and Microanalysis , Volume 6 , Issue S2: Proceedings: Microscopy & Microanalysis 2000, Microscopy Society of America 58th Annual Meeting, Microbeam Analysis Society 34th Annual Meeting, Microscopical Society of Canada/Societe de Microscopie de Canada 27th Annual Meeting, Philadelphia, Pennsylvania August 13-17, 2000 , August 2000 , pp. 272 - 273
Copyright
Copyright © Microscopy Society of America

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