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Journal of Bacteriology, April 2003, p. 2465-2474, Vol. 185, No. 8
0021-9193/03/$08.00+0 DOI: 10.1128/JB.185.8.2465-2474.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Miami, Florida
Received 20 September 2002/ Accepted 24 January 2003
Many DNA viruses concatemerize their genomes as a prerequisite to packaging into capsids. Concatemerization arises from either replication or homologous recombination. Replication is already the target of many antiviral drugs, and viral recombinases are an attractive target for drug design, particularly for combination therapy with replication inhibitors, due to their important supporting role in viral growth. To dissect the molecular mechanisms of viral recombination, we and others previously identified a family of viral nucleases that comprise one component of a conserved, two-component viral recombination system. The nuclease component is related to the exonuclease of phage
and is common to viruses with linear double-stranded DNA genomes. To test the idea that these viruses have a common strategy for recombination and genome concatemerization, we isolated the previously uncharacterized 34.1 gene from Bacillus subtilis phage SPP1, expressed it in Escherichia coli, purified the protein, and determined its enzymatic properties. Like
exonuclease, Chu (the product of 34.1) forms an oligomer, is a processive alkaline exonuclease that digests linear double-stranded DNA in a Mg2+-dependent reaction, and shows a preference for 5'-phosphorylated DNA ends. A model for viral recombination, based on the phage
Red recombination system, is proposed.
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