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Journal of Virology, January 2006, p. 440-450, Vol. 80, No. 1
0022-538X/06/$08.00+0 doi:10.1128/JVI.80.1.440-450.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Departments of Medicine and Microbiology and Molecular Genetics, Harvard Medical School at the Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215
Received 21 July 2005/ Accepted 12 October 2005
In vitro studies of herpes simplex virus type 1 (HSV-1) viruses containing mutations in core sequences of the viral origins of DNA replication, oriL and oriS, that eliminate the ability of these origins to initiate viral-DNA synthesis have demonstrated little or no effect on viral replication in cultured cells, leading to the conclusion that the two types of origins are functionally redundant. It remains unclear, therefore, why origins that appear to be redundant are maintained evolutionarily in HSV-1 and other neurotropic alphaherpesviruses. To test the hypothesis that oriL and oriS have distinct functions in the HSV-1 life cycle in vivo, we determined the in vivo phenotypes of two mutant viruses, DoriL-ILR and DoriS-I, containing point mutations in oriL and oriS site I, respectively, that eliminate origin DNA initiation function. Following corneal inoculation of mice, tear film titers of DoriS-I were reduced relative to wild-type virus. In all other tests, however, DoriS-I behaved like wild-type virus. In contrast, titers of DoriL-ILR in tear film, trigeminal ganglia (TG), and hindbrain were reduced and mice infected with DoriL-ILR exhibited greatly reduced mortality relative to wild-type virus. In the TG explant and TG cell culture models of reactivation, DoriL-ILR reactivated with delayed kinetics and, in the latter model, with reduced efficiency relative to wild-type virus. Rescuant viruses DoriL-ILR-R and DoriS-I-R behaved like wild-type virus in all tests. These findings demonstrate that functional differences exist between oriL and oriS and reveal a prominent role for oriL in HSV-1 pathogenesis.
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