Transcriptional and translational expression kinetics of the bovine herpesvirus 1 UL51 homologue gene

We characterized the expression kinetics of the transcript and protein generated from the bovine herpesvirus 1 (BHV1) homologue of the herpes simplex virus 1 (HSV1) UL51 gene. The BHV1 UL51 ORF, located at positions 7236→7967 of the viral genome, generated a major 1.05 kb transcript accumulating at very low abundance as soon as 3 h post-infection (p.i.), after which its levels increased to reach a plateau from 6 to 12 h p.i., and then slowly decreased up to 24 h p.i. As determined by S1 nuclease protection assays, UL51 transcription initiated at two distinct sites located at 191 and 196 bases upstream from the initiation codon, corresponding to positions 7045 and 7040 of the viral genome, respectively. Western blotting of BHV1-infected protein cell lysates, using a BHV1-specific antiserum generated against a recombinant protein expressed in Escherichia coli, detected a 28 kDa protein of the expected size (24 985 Da) whose expression kinetics followed that of its transcript. As evidenced by in situ immunofluorescence assays, the protein mainly localized to the cytoplasm and the perinuclear region of infected cells. In contrast to HSV1 UL51 which is classified as a γ2 gene, BHV1 UL51 belongs to viral genes of the γ1 class as expression of its transcript is partially dependent on viral DNA synthesis.