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The mechanism of cruciform formation in supercoiled DNA: initial opening of central basepairs in salt-dependent extrusion.
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MedLine Citation:
PMID:  3697079     Owner:  NLM     Status:  MEDLINE    
There are two alternative pathways by which inverted repeat sequences in supercoiled DNA molecules may extrude cruciform structures, called C-type and S-type. S-type cruciforms, which form the great majority, are characterised by absolute requirement for cations to promote extrusion, which then proceeds at higher temperatures and with lower activation parameters than for C-type cruciforms. The mechanism proposed for S-type extrusion involves an initial opening of basepairs limited to the centre of the inverted repeat, formation of intra-strand basepairing and a four-way junction, and finally branch migration to the fully extruded cruciform. The model predicts that central sequence changes will be more kinetically significant than those removed from the centre. We have studied the kinetics of cruciform extrusion by a series of inverted repeats related to that of pIRbke8 by either one or two mutations in the symmetric unit. We find that mutations in the central 8 to 10 nucleotides may profoundly affect extrusion rates--the fastest being 2000-fold faster than the slowest, whereas mutations further from the centre affect rates to a much smaller extent, typically up to ten-fold. These data support the proposed mechanism for extrusion via central opening.
A I Murchie; D M Lilley
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Nucleic acids research     Volume:  15     ISSN:  0305-1048     ISO Abbreviation:  Nucleic Acids Res.     Publication Date:  1987 Dec 
Date Detail:
Created Date:  1988-02-23     Completed Date:  1988-02-23     Revised Date:  2010-09-10    
Medline Journal Info:
Nlm Unique ID:  0411011     Medline TA:  Nucleic Acids Res     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  9641-54     Citation Subset:  IM    
Department of Biochemistry, University, Dundee, UK.
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MeSH Terms
Base Sequence / drug effects
DNA, Superhelical* / drug effects
Models, Genetic
Nucleic Acid Conformation* / drug effects
Plasmids / drug effects
Sodium Chloride* / pharmacology
Reg. No./Substance:
0/DNA, Superhelical; 7647-14-5/Sodium Chloride

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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Journal Information
Journal ID (nlm-ta): Nucleic Acids Res
ISSN: 0305-1048
ISSN: 1362-4962
Article Information
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Print publication date: Day: 10 Month: 12 Year: 1987
Volume: 15 Issue: 23
First Page: 9641 Last Page: 9654
ID: 306521
PubMed Id: 3697079

The mechanism of cruciform formation in supercoiled DNA: initial opening of central basepairs in salt-dependent extrusion.
A I Murchie
D M Lilley
Department of Biochemistry, University, Dundee, UK.

Article Categories:
  • Research Article

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