J. Virol., Mar 1995, 1377-1388, Vol 69, No. 3
MA Hardwicke and PA Schaffer
The herpes simplex virus type 1 genome contains three origins of DNA
replication: two copies of oriS and one copy of oriL. Although oriS has
been characterized extensively, characterization of oriL has been severely
limited by the inability to amplify oriL sequences in an undeleted form in
Escherichia coli. We report the successful cloning of intact oriL sequences
in an E. coli strain, SURE, which contains mutations in a series of genes
involved in independent DNA repair pathways shown to be important in the
rearrangement and deletion of DNA containing irregular structures such as
palindromes. The oriL- containing clones propagated in SURE cells contained
no deletions, as determined by Southern blot hybridization and DNA sequence
analysis, and were replication competent in transient DNA replication
assays. Deletion of 400 bp of flanking sequences decreased the replication
efficiency of oriL twofold in transient assays, demonstrating a role for
flanking sequences in enhancing replication efficiency. Comparison of the
replication efficiencies of an 822-bp oriS-containing plasmid and an 833-bp
oriL-containing plasmid demonstrated that the kinetics of replication of
the two plasmids were similar but that the oriL- containing plasmid
replicated 60 to 70% as efficiently as the oriS- containing plasmid at both
early and late times after infection with herpes simplex virus type 1. The
virus-specified origin-binding protein (OBP) and a cellular factor(s)
(OF-1) have been shown in gel mobility shift experiments to bind specific
sequences in oriS (C.E. Dabrowski, P. Carmillo, and P.A. Schaffer, Mol.
Cell. Biol. 14:2545-2555, 1994; C.E. Dabrowski and P.A. Schaffer, J. Virol.
65:3140-3150, 1991). Although the nucleotides required for the binding of
OBP to OBP binding site I in oriL and oriS are the same, a single
nucleotide difference distinguishes OBP binding site III in the two
origins. The nucleotides adjacent to oriS sites I and III have been shown
to be important for the binding of OF-1 to oriS site I. Several nucleotide
differences exist in these sequences in oriL and oriS. Despite these minor
nucleotide differences, the protein-DNA complexes that formed with oriL and
oriS sites I and III were indistinguishable when extracts of infected and
uninfected cells were used as the source of protein. Furthermore, the
results of competition analysis suggest that the proteins involved in
protein-DNA complex formation with sites I and III of the two origins are
likely the same.
Copyright © 1995, American Society for Microbiology
Cloning and characterization of herpes simplex virus type 1 oriL: comparison of replication and protein-DNA complex formation by oriL and oriS
Division of Molecular Genetics, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
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