Transcriptional Analysis of the Short Segment of the Feline Herpesvirus Type 1 Genome and Insertional Mutagenesis of a Unique Reading Frame

Transcription mapping was performed in the short region of the feline herpesvirus type 1 (FHV-1) genome as a first approach to the functional analysis of open reading frames encoding the homologs of the herpes simplex virus type 1 (HSV1) gD, gI, gE, US9, and probably also US8.5 All reading frames appeared to be transcribed. Transcripts were grouped into two nested RNA sets; namely, the coterminal transcripts of gD and gI and the coterminal transcripts of gE, US8.5, and US9. This situation was similar to that found in the equivalent region of HSV-1. The FHV-1 ORFs US8.5 and US9 have not been described previously. Sequence analysis and comparison of the putative polypeptide encoded by US8.5 revealed that this ORF was unique to FHV-1. However, US8.5 of FHV-1 might be functionally related to its positional homologs in HSV-1 and equine herpesvirus type 1. In all three viruses, US8.5 does not seem to be critical for virus propagation in cell culture. This was shown for FHV-1 by isolating a mutant containing an insertion in US8.5 and comparing its growth properties in cell culture to those of the parent virus G2620. With regard to US9, conscientious amino acid sequence alignment of FHV-1 US9 and homologs in related herpesviruses suggests that this particular protein could contribute to the virus infectivity in vivo. This speculation was based on the highly conserved C-terminus of US9, starting with a characteristic YYSES motif and followed by a nuclear target sequence and a transmembrane region.