Existence of transdominant and potentiating mutants of UL9, the herpes simplex virus type 1 origin-binding protein, suggests that levels of UL9 protein may be regulated during infection.
UL9 is a multifunctional protein required for herpes simplex virus type 1 (HSV-1) replication in vivo. UL9 is a member of the superfamily II helicases and exhibits helicase and origin-binding activities. We have previously shown that mutations in the conserved helicase motifs of UL9 can have either a transdominant or potentiating effect on the plaque-forming ability of infectious DNA from wild-type virus (A. J. Malik and S. K. Weller, J. Virol. 70:7859-7866, 1996). In this paper, the mechanisms of transdominance and potentiation are explored. We show that the motif V mutant protein containing a G to A substitution at residue 354 is unstable when expressed by transfection and is either processed to a 38-kDa N-terminal fragment or degraded completely. The overexpression of the MV mutant protein is able to influence the steady-state protein levels of wild-type UL9 and to override the inhibitory effects of wild-type UL9. Potentiation correlates with the ability of the UL9 variants containing the G354A mutation to be processed or degraded to the 38-kDa form. We propose that the MV mutant protein is able to interact with full-length UL9 and that this interaction results in a decrease in the steady-state levels of UL9, which in turn leads to enhanced viral infection. Furthermore, we demonstrate that inhibition of HSV-1 infection can be obtained by overexpression of full-length UL9, the C-terminal third of the protein containing the origin-binding domain, or the N-terminal two-thirds of UL9 containing the conserved helicase motifs and the putative dimerization domain. Our results suggest that transdominance can be mediated by overexpression, origin-binding activity, and dimerization, whereas potentiation is most likely caused by the ability of the UL9 MV mutant to influence the steady-state levels of wild-type UL9. Taken together, the results presented in this paper suggest that the regulation of steady-state levels of UL9 may play an important role in controlling viral infection.
Marintcheva
Boriana
B
Department of Microbiology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
Weller
Sandra K
SK
D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002522:Chlorocebus aethiops; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D004279:DNA, Viral / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D005814:Genes, Viral; D018259:Herpesvirus 1, Human / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology*; D008954:Models, Biological; D009154:Mutation; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010957:Plasmids / Q000235:genetics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018411:Spodoptera; D014162:Transfection; D014709:Vero Cells; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D014779:Virus Replication
D004279:DNA, Viral; D004268:DNA-Binding Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D014764:Viral Proteins; C064565:UL9 protein, Human herpesvirus 1; D004265:DNA Helicases