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Journal of Virology, December 2003, p. 12412-12420, Vol. 77, No. 23
0022-538X/03/$08.00+0     DOI: 10.1128/JVI.77.23.12412-12420.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Template Switches during Plus-Strand DNA Synthesis of Duck Hepatitis B Virus Are Influenced by the Base Composition of the Minus-Strand Terminal Redundancy

Jeffrey W. Habig and Daniel D. Loeb*

McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison, Wisconsin 53706

Received 22 July 2003/ Accepted 25 August 2003

Two template switches are necessary during plus-strand DNA synthesis of the relaxed circular (RC) form of the hepadnavirus genome. The 3' end of the minus-strand DNA makes important contributions to both of these template switches. It acts as the donor site for the first template switch, called primer translocation, and subsequently acts as the acceptor site for the second template switch, termed circularization. Circularization involves transfer of the nascent 3' end of the plus strand from the 5' end of the minus-strand DNA to the 3' end, where further elongation can lead to production of RC DNA. In duck hepatitis B virus (DHBV), a small terminal redundancy (5'r and 3'r) on the ends of the minus-strand DNA has been shown to be important, but not sufficient, for circularization. We investigated what contribution, if any, the base composition of the terminal redundancy made to the circularization process. Using a genetic approach, we found a strong positive correlation between the fraction of A and T residues within the terminal redundancy and the efficiency of the circularization process in those variants. Additionally, we found that the level of in situ priming increases, at the expense of primer translocation, as the fraction of A and T residues in the 3'r decreases. Thus, a terminal redundancy rich in A and T residues is important for both plus-strand template switches in DHBV.

* Corresponding author. Mailing address: McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, 1400 University Ave., Madison, WI 53706. Phone: (608) 262-1260. Fax: (608) 262-2824. E-mail: loeb{at}oncology.wisc.edu.

Journal of Virology, December 2003, p. 12412-12420, Vol. 77, No. 23
0022-538X/03/$08.00+0     DOI: 10.1128/JVI.77.23.12412-12420.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.





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