Bovine herpesvirus 4 genome: cloning, mapping and strain variation analysis.

The restriction map of the bovine herpesvirus 4 (BHV-4) genome (V. Test strain) was established for the restriction enzymes EcoRI, BamHI and HindIII by analysis of clones from a lambda library (Sau3AI partial digestion) and from a plasmid library (EcoRI fragments). One genome unit was defined as the length of the unique central part, flanked at both ends by one of the terminal tandem repeats called polyrepetitive DNA (prDNA) and was estimated to be 113 +/- 2 kbp. A restriction map of the prDNA of the V. Test strain showed internal 200 bp tandem repeats of different sequences. This region in the prDNA was highly polymorphic between BHV-4 strains, even in a viral DNA preparation from a plaque-purified strain. The right junction between the repeated and the unique sequence of the genome occurred at an almost constant site, but the left junction contained a modified prDNA and was variable between BHV-4 strains. The unique central part of the genome was very similar in the four strains under consideration, with a few variations due to the presence or absence of a restriction site and four length variations were observed, located at positions 0.006 to 0.034 (left end), 0.211 to 0.225, 0.864 to 0.881 and 0.962 to 0.984 (right end). The total length variation of 1 genome unit does not exceed 1 kbp.