Genetic relatedness and colinearity of genomes of equine herpesvirus types 1 and 3.

The arrangement and location of homologous DNA sequences within the genomes of equine herpesvirus type 1 (EHV-1) and EHV-3 were investigated by using Southern blot hybridization analyses conducted under stringent conditions. Recombinant plasmid libraries comprising 95 and 84% of the EHV-1 and EHV-3 genomes, respectively, were labeled with 32P-deoxynucleotides by nick translation and were used as probes in filter hybridization studies. The DNA homology between the EHV-1 and EHV-3 genomes was dispersed throughout the genomes in a colinear arrangement. Significant hybridization was detected between the EHV-1 short region inverted repeat sequences, which are known to encode immediate early transcripts, and the corresponding EHV-3 inverted repeat sequences. Interestingly, probes derived from the EHV-1 heterogeneous region, which is adjacent to the EHV-1 short region, hybridized strongly to EHV-3 DNA sequences within a similar genomic location, but did not reveal any corresponding heterogeneity within the EHV-3 genome. Our results demonstrated that there is a highly conserved evolutionary relationship between EHV-1 and EHV-3 and provided the foundation for further investigations to determine whether similarities in protein function underpin the genetic relatedness between these two herpesviruses.