Identification of a novel protein encoded by the latency-related gene of bovine herpesvirus 1

The latency-related (LR) RNA encoded by bovine herpesvirus 1 (BHV-1) is abundantly expressed and alternatively spliced in trigeminal ganglia. A mutant BHV-1 strain that contains three stop codons at the beginning of LR open reading frame (ORF)-2 (LR mutant virus) does not express ORF-2 or an adjacent reading frame that lacks an initiating ATG (RF-C). Calves latently infected with wild-type (wt) BHV-1, but not with the LR mutant virus, reactivate from latency, indicating that proteins encoded by the LR gene regulate the latency-reactivation cycle. The LR gene also contains another large ORF (ORF-1) that is approximately 200 bp downstream of stop codons inserted at the N-terminus of ORF-2. To test whether the LR mutant virus can expresses ORF-1, the authors developed antiserum directed against ORF-1. The ORF-1 antiserum recognizes specific proteins in bovine cells productively infected with wt BHV-1. ORF-1 protein expression is reduced, but not blocked, when bovine cells are infected with the LR mutant virus. Confocal microscopy demonstrated ORF-1 is present in the cytoplasm and nucleus of productively infected cells, whereas RF-C or a fusion protein containing RF-C localizes to the cytoplasm. Trigeminal ganglia from calves latently infected with wt BHV-1 contain neurons specifically stained with the ORF-1 antiserum. These studies suggest ORF-1 expression may be important for the BHV-1 latency-reactivation cycle.