Identification of a novel bovine herpesvirus 1 transcript containing a small open reading frame that is expressed in trigeminal ganglia of latently infected cattle.

Bovine herpesvirus 1 (BHV-1), like other Alphaherpesvirinae subfamily members, establishes latency in sensory neurons. The latency-related (LR) RNA is abundantly expressed during latency, and expression of an LR protein is required for the latency reactivation cycle in cattle. Within LR promoter sequences, a 135-amino-acid open reading frame (ORF) was identified, ORF-E, that is antisense to the LR RNA. ORF-E is also downstream of the gene encoding the major viral transcriptional activator, bICP0. Strand-specific reverse transcription-PCR demonstrated that a transcript containing ORF-E was consistently expressed in trigeminal ganglia (TG) of latently infected calves, productively infected cultured cells, and acutely infected calves. As expected, a late transcript encoding glycoprotein C was not detected in TG of latently infected calves. The ORF-E transcript is polyadenylated and is expressed early when cultured bovine cells are productively infected. Protein coding sequences containing ORF-E were fused to green fluorescent protein (GFP) to examine the cellular localization of the putative protein. In transiently transfected mouse neuroblastoma (neuro-2A) and human neuroblastoma (SK-N-SH) cells, the ORF-E/GFP fusion protein was detected in discreet domains within the nucleus. In contrast, the ORF-E/GFP fusion protein was detected in the cytoplasm and nucleus of rabbit skin cells and bovine kidney cells. As expected, the GFP protein was expressed in the cytoplasm and nucleus of transfected cells. These studies indicate that the ORF-E transcript is consistently expressed during latency. We suggest that the ORF-E gene regulates some aspect of the latency reactivation cycle.