J Biol Chem, Vol. 273, Issue 20, 12120-12127, May 15, 1998
The Role of Negative Superhelicity and Length of Homology in the
Formation of Paranemic Joints Promoted by RecA Protein
Brian C.
Wong
,
Sung-Kay
Chiu, and
Samson A.
Chow
From the Department of Biochemistry, University of
Hong Kong, Hong Kong and the Department of Molecular and Medical
Pharmacology, UCLA School of Medicine,
Los Angeles, California 90095
Escherichia coli RecA protein pairs
homologous DNA molecules to form paranemic joints when there is an
absence of a free end in the region of homologous contact. Paranemic
joints are a key intermediate in homologous recombination and are
important in understanding the mechanism for a search of homology. The
efficiency of paranemic joint formation depended on the length of
homology and the topological forms of the duplex DNA. The presence of
negative superhelicity increased the pairing efficiency and reduced the minimal length of homology required for paranemic joint formation. Negative superhelicity stimulated joint formation by favoring the
initial unwinding of duplex DNA that occurred during the homology search and was not essential in the maintenance of the paired structure. Regardless of length of homology, formation of paranemic joints using circular duplex DNA required the presence of more than six
negative supercoils. Above six negative turns, an increasing degree of
negative superhelicity resulted in a linear increase in the pairing
efficiency. These results support a model of two distinct kinds of DNA
unwinding occurring in paranemic joint formation: an initial unwinding
caused by heterologous contacts during synapsis and a later one during
pairing of the homologous molecules.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
