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J. Virol., Oct 1997, 7791-7798, Vol 71, No. 10
YT Hwang, BY Liu, DM Coen and CB Hwang
The herpes simplex virus DNA polymerase catalytic subunit, which has
intrinsic polymerase and 3'-5' exonuclease activities, contains sequence
motifs that are homologous to those important for 3'-5' exonuclease
activity in other polymerases. The role of one such motif, Exo III, was
examined in this study. Mutated polymerases containing either a single
tyrosine-to-histidine change at residue 577 or this change plus an aspartic
acid-to-alanine at residue 581 in the Exo III motif exhibited defective or
undetectable exonuclease activity, respectively, yet retained substantial
polymerase activity. Despite the defects in exonuclease activity, the
mutant polymerases were able to support viral replication in transient
complementation assays, albeit inefficiently. Viruses replicated via the
action of these mutant polymerases exhibited substantially increased
frequencies of mutants resistant to ganciclovir. Furthermore, when the Exo
III mutations were incorporated into the viral genome, the resulting mutant
viruses displayed only modestly defect in replication in Vero cells and
exhibited substantially increased mutation frequencies. The results suggest
that herpes simplex virus can replicate despite severely impaired
exonuclease activity and that the 3'-5' exonuclease contributes
substantially to the fidelity of viral DNA replication.
Copyright © 1997, American Society for Microbiology
Effects of mutations in the Exo III motif of the herpes simplex virus DNA polymerase gene on enzyme activities, viral replication, and replication fidelity
Department of Microbiology and Immunology, Medical College, State University of New York, Syracuse 13210, USA.
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