Characterization of the bovine herpesvirus 1 homolog of the herpes simplex virus 1 UL24 open reading frame.

An open reading frame (ORF) of 293 codons which partially overlaps the bovine herpesvirus 1 (BHV1) thymidine kinase (tk) ORF in a head-to-head orientation has been identified by nucleotide sequence analysis. The predicted amino acid sequence of this ORF exhibits an overall identity of 38.1% with that of the herpes simplex virus type 1 (HSV1) UL24 ORF as well as an 80.7% identity with the 57-amino-acid consensus sequence found in the UL24-like ORFs of eight herpesviruses (Jacobson et al., J. Virol, 49, 947-959, 1989). We have therefore designated this BHV1 ORF as the homolog of the HSV1 UL24 ORF with which it also shares a common position and orientation relative to the tk ORF. The BHV1 UL24-like ORF is contained within a 5.2-kb RNA transcript initiating within the tk ORF and is the largest in a group of four 3'-coterminal transcripts. This transcript pattern closely resembles that observed in HSV1-infected cells where five transcripts, the two largest of which contain the UL24 ORF, appear to be 3'-coterminal. In contrast to HSV1 mutants with lesions in the UL24 ORF, a BHV1 deletion mutant which failed to produce detectable levels of the 5.2-kb transcript grew nearly as well as wild-type virus.