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Journal of Virology, September 2005, p. 11291-11299, Vol. 79, No. 17
0022-538X/05/$08.00+0     doi:10.1128/JVI.79.17.11291-11299.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

The UL7 Gene of Pseudorabies Virus Encodes a Nonessential Structural Protein Which Is Involved in Virion Formation and Egress

Institutes of Molecular Biology,¹ Infectology, Friedrich-Loeffler-Institut, 17493 Greifswald-Insel Riems, Germany²

Received 29 April 2005/ Accepted 14 June 2005

Homologues of the UL7 gene of herpes simplex virus type 1 are conserved in alpha-, beta-, and gammaherpesviruses. However, little is known about their functions. Using a monospecific rabbit antiserum raised against a bacterial fusion protein, we identified the UL7 gene product of the neurotropic alphaherpesvirus pseudorabies virus (PrV). In Western blot analyses of infected cells and purified PrV particles the serum specifically detected a 29-kDa protein, which matches the calculated mass of the 266-amino-acid translation product of PrV UL7. For functional analysis, UL7 was deleted by mutagenesis of an infectious full-length clone of the PrV genome in Escherichia coli. The obtained recombinant PrV-UL7F was replication competent in rabbit kidney cells, but maximum virus titers were decreased nearly 10-fold and plaque diameters were reduced by ca. 60% compared to wild-type PrV. Electron microscopy of infected cells revealed that in the absence of UL7, formation and nuclear egress of nucleocapsids were not affected, whereas secondary envelopment of cytoplasmic nucleocapsids appeared to be delayed and release of mature virions was less efficient. The observed replication defects were corrected by repair of the viral UL7 gene or by propagation of PrV-UL7F in UL7-expressing cells. PrV-UL7F was moderately attenuated in mice. Compared to wild-type virus, mean survival times were prolonged from 2 to 3 days after intranasal infection. However, neuroinvasion and transneuronal spread of PrV were not abolished in the absence of UL7. Thus, UL7 encodes a virion protein of PrV, which plays a role during virion maturation and egress both in vitro and in vivo.

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