Journal of Virology, February 2000, p. 1587-1592, Vol. 74, No. 3
Department of Pediatrics, Medical College of
Virginia Campus of Virginia Commonwealth University, Richmond,
Virginia 23298-0163
Received 13 August 1999/Accepted 25 October 1999
Herpesviruses have large double-stranded linear DNA genomes that
are formed by site-specific cleavage from complex concatemeric intermediates. In this process, only one of the two genomic ends are
formed on the concatemer. Although the mechanism underlying this
asymmetry is not known, one explanation is that single genomes are
cleaved off of concatemer ends in a preferred direction. This implies
that cis elements control the direction of packaging. Two
highly conserved cis elements named pac1 and
pac2 lie near opposite ends of herpesvirus genomes and are
important for cleavage and packaging. By comparison of published
reports and by analysis of two additional herpesviruses, we found that
pac2 elements lie near the ends formed on replicative
concatemers of four herpesviruses: herpes simplex virus type 1, equine
herpesvirus 1, guinea pig cytomegalovirus, and murine cytomegalovirus.
Formation of pac2 ends on concatemers depended on terminal
cis sequences, since ectopic cleavage sites engineered into
the murine cytomegalovirus genome mediated formation of
pac2 ends on concatemers regardless of the orientation of
their insertion. These findings are consistent with a model in which
pac2 elements at concatemer ends impart a directionality to
concatemer packaging by binding proteins that initiate insertion of
concatemer ends into empty capsids.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
The Ends on Herpesvirus DNA Replicative Concatemers
Contain pac2 cis Cleavage/Packaging Elements and Their
Formation Is Controlled by Terminal cis Sequences
*
Corresponding author. Mailing address: Department of
Pediatrics, Medical College of Virginia Campus of Virginia Commonwealth University, P.O. Box 980163, Richmond, VA 23298-0163. Phone: (804) 828-0132. Fax: (804) 828-6455. E-mail:
mmcvoy{at}hsc.vcu.edu.
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