Molecular pathogenesis of equine coital exanthema: restriction endonuclease digestions of EHV-3 DNA and indications of a unique XbaI cleavage site.

Equine herpesvirus type 3 (EHV-3) DNA, isolated from purified virions of the large-plaque strain, was digested with the restriction endonucleases XbaI, Bg/II, EcoRI, and HindIII. Several lines of evidence indicated that the DNA extracted from purified virions was composed of long (L) and short (S) components and was present as two isomeric forms, P and IS. The evidence included: (i) after electrophoresis on agarose gels, the summed molecular weights of the digestion products exceeded that expected from intact, unit size DNA; (ii) quantitative measurements of radioactivity (molar ratios) indicated 'minor bands' (0.5 M) interspersed among the major (1.0 M) bands; and (iii) a brief digestion with lambda-5'-exonuclease, prior to digestion with restriction endonuclease, resulted in the loss of some submolar and molar ratio bands, indicative of three termini. A preliminary fragment linkage map of the XbaI digestion products revealed EHV-3 DNA to contain only one recognition site in the unique sequence of the S component. From this linkage map, the size of the S component was deduced to be (22.3 +/- 5) X 10(6) molecular weight.