The UL4 gene of pseudorabies virus encodes a minor infected-cell protein that is dispensable for virus replication.
Although homologues of the open reading frame (ORF) UL4 of herpes simplex virus 1 (Human herpesvirus 1) have been found in the genomes of all hitherto-analysed alphaherpesviruses, little is known about their function. In a project to analyse systematically, in an isogenic and standardized assay system, the gene products of the alphaherpesvirus pseudorabies virus (PrV; Suid herpesvirus 1), the PrV UL4 gene product was identified using a monospecific rabbit antiserum prepared against a bacterial fusion protein. Western blot and immunofluorescence analyses revealed that the 146 codon UL4 ORF of PrV was translated into a nuclear 15 kDa protein which was detectable from 6 h after infection of rabbit kidney cells, but was not found in purified virus particles. For functional analysis, a UL4-negative virus recombinant (PrV-DeltaUL4F) was generated by mutagenesis of an infectious full-length clone of the PrV genome in E. coli. PrV-DeltaUL4F was replication-competent in rabbit kidney cells, and plaque formation was not affected by the mutation. However, maximum virus titres of PrV-DeltaUL4F were decreased about fivefold compared with wild-type PrV, and electron microscopy of infected cells demonstrated an impairment of release of mature virions. This growth defect of PrV-DeltaUL4F could be corrected completely by propagation in UL4-expressing cells. Correlating with the inconspicuous in vitro phenotype, neurovirulence of PrV-DeltaUL4F was also not affected significantly. Thus, UL4 encodes a non-structural protein of PrV that enhances virion formation but is not essential for PrV replication in vitro or in vivo.
Fuchs
Walter
W
Institute of Molecular Biology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany.
Granzow
Harald
H
Institute of Infectology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany.
Klopfleisch
Robert
R
Institute of Infectology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany.
Klupp
Barbara G
BG
Institute of Molecular Biology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany.
Mettenleiter
Thomas C
TC
Institute of Molecular Biology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany.
D000818:Animals; D002460:Cell Line; D004926:Escherichia coli / Q000235:genetics; D005814:Genes, Viral; D011558:Herpesvirus 1, Suid / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology*; D008854:Microscopy, Electron; D016296:Mutagenesis; D016366:Open Reading Frames; D010957:Plasmids / Q000235:genetics; D011817:Rabbits; D014162:Transfection; D014764:Viral Proteins / Q000235:genetics* / Q000502:physiology*; D014774:Virulence / Q000235:genetics / Q000502:physiology; D014779:Virus Replication / Q000235:genetics* / Q000502:physiology*
C088324:UL4 protein, swine herpes virus; D014764:Viral Proteins