Equine herpesvirus 5: comparisons with EHV2 (equine cytomegalovirus), cloning, and mapping of a new equine herpesvirus with a novel genome structure.

A new equine herpesvirus, provisionally designated equine herpesvirus 5 (EHV5; Browning and Studdert (1987) J. Gen. Virol. 68, 1441-1447), was examined for the degree of genomic difference from equine herpesvirus 2 (EHV2) by Southern hybridizations. EHV5 and EHV2 whole genomic DNA probes were highly specific for homologous DNA only, indicating that significant genomic difference exists between the two viruses. Restriction endonuclease analysis of EHV5 strain 2-141 (EHV5.2-141) revealed that the genome is 179 kb and exists as a single isomer. Clones representing 82% of the genome were obtained and used to construct restriction maps for four restriction endonucleases. Hybridization experiments indicated that the EHV5.2-141 genome does not contain large terminal or internal repeats, although some evidence for very short repeated sequences in the genomic termini was obtained. Such a genome structure makes EHV5 unique among the equine herpesviruses but similar to the mouse, rat, and guinea pig cytomegaloviruses and the tupaiid herpesvirus. Sequence analysis of one of the genomic termini of EHV5.2-141 revealed the presence of a 30-bp sequence (pac-1; Deiss et al. (1986) J. Virol. 59, 605-618) which is highly conserved among herpesviruses.