The serine-threonine protein kinase encoded by US3 gene (pUS3) of
alphaherpesviruses was shown to modulate actin reorganization, cell-to-cell
spread, and virus egress in a number of virus species. However, the role of
the US3 orthologues of equine herpesvirus type 1 and 4 (EHV-1 and EHV-4) has
not yet been studied. Here, we show that US3 is not essential for virus
replication in vitro. However, growth rates and plaque diameters of a
US3-deleted EHV-1 and a mutant in which the catalytic active site was
destroyed were significantly reduced when compared with parental and revertant
viruses or a virus in which EHV-1 US3 was replaced with the corresponding
EHV-4 gene. The reduced plaque sizes were consistent with accumulation of
primarily enveloped virions in the perinuclear space of the US3-negative
EHV-1, a phenotype that was also rescued by the EHV-4 orthologue. Furthermore,
actin stress fiber disassembly was significantly more pronounced in cells
infected with parental EHV-1, revertant, or the recombinant EHV-1 expressing
EHV-4 US3. Finally, we observed that deletion of US3 in EHV-1 did not affect
the expression of adhesion molecules on the surface of infected cells