THE US3-ENCODED PROTEIN-KINASE FROM PSEUDORABIES VIRUS AFFECTS EGRESSOF VIRIONS FROM THE NUCLEUS

We examined the influence of inactivation of various genes located in the unique short (U-s) region of pseudorabies virus on virus replicati on and assembly in porcine nasal mucosa explant cultures. The followin g strains were used: the virulent wild-type strain NIA-3, and strains derived from NIA-3 containing a mutation inactivating the genes encodi ng either the US3-encoded protein kinase (PK), gG, gD, gI, gE, the 28 kDa ('28K') protein (single mutant), or the 28K and 11 kDa ('11K') pro teins (double mutant). In addition a wild-type rescuant was used, whic h was generated by marker rescue from a PK- mutant. All virus strains infected nasal epithelium and had invaded the stroma after approximate ly 24 h. The morphogenesis in nasal epithelium cells of two PK- mutant s showed the most striking differences compared to the parent NIA-3 st rain and the other mutant strains. The changes could be ascribed to th e US3-encoded PK because the rescue mutant showed a similar morphogene sis to wild-type NIA-3. The transmembrane transport of the PK- mutants was impaired at the outer nuclear membrane which resulted in an accum ulation of virions in the perinuclear space. These results suggest tha t proteins, phosphorylated by the US3-encoded PK, are involved in debu dding of virus particles at the outer nuclear membrane. This defect in the transport of the US3 mutant probably explains their reduced repli cation in vitro. The gG(-), gD(-), gI(-), gE(-), 28K(-) and 11K(-) mut ant strains showed minor or no changes in viral assembly. Thus the rep orted decreased virulence of the gD(-), gI(-) and gE(-) mutants was, i n contrast to that of the PK-mutants, not associated with clear altera tions in morphogenesis.