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

This research article examines a new equine herpesvirus, EHV5, comparing its genetic differences with another known equine herpesvirus, EHV2. The paper also reports the successful cloning and mapping of EHV5, which features a unique genome structure without large internal or terminal repeats, a trait it shares with a few other viruses.

Detailed Comparison of EHV5 and EHV2

• The research begins with a comparative analysis of EHV5 and EHV2, both forms of the equine herpesvirus. In this study, the researchers perform a series of Southern hybridizations, a technique used to check for the presence of specific DNA sequences within a DNA sample.
• The experiments using EHV5 and EHV2 genomic DNA probes revealed a striking genomic difference between the two viruses, suggesting they differ significantly at the DNA level.

Molecular Characterization of EHV5

• As part of the characterization of EHV5, especially the strain 2-141 (EHV5.2-141), the authors also conducted a restriction endonuclease analysis. This biochemical technique is typically used to cut DNA molecules at specific sites.
• The result of this analysis revealed that the EHV5.2-141 genome is 179 kilobases (kb) long and exists as a singular isomer, or a molecule with the same molecular formula as another molecule, but with a different chemical structure.
• The scientists were able to clone about 82% of the genome and use these clones to construct restriction maps, which offer a detailed overview of the locations of genes and other important features on a DNA molecule.

Unique Genome Structure

• Further examination revealed unusual characteristics of the EHV5.2-141 genome. Unlike many other equine herpesviruses, EHV5 does not contain large internal or terminal repeat sequences. Some evidence of very short repeated sequences at the genomic ends was found, though.
• This absence of repeat sequences makes EHV5 unique among equine herpesviruses but makes it similar to other viruses, like the mouse, rat, guinea pig cytomegaloviruses, and the tupaiid herpesvirus.

Highly Conserved Sequence

• Finally, the sequence analysis of one of the EHV5.2-141 genomic termini revealed a highly conserved 30-base pair (bp) sequence. A ‘conserved’ sequence is a DNA sequence that remains unchanged across different species, indicating an important biological function. In this case, the sequence, called pac-1, is also found in other herpesviruses, pointing towards an evolutionary connection.