Pseudorabies virus displays variable numbers of a repeat unit adjacent to the 3' end of the glycoprotein gII gene

The coding region of the glycoprotein complex gII of pseudorabies virus (PRV) is located in the unique long part of the genome on Sa/I subfragments 1A and 1G of BamHI fragment 1 (map units 0.105 to 0.130). Fragment 1G which includes the 3′ end of the gII gene displays a size heterogeneity among different PRV strains and also within plaque isolates of a given strain. To reveal the cause of this heterogeneity and whether it might affect the gII-coding region we sequenced different 1G fragments of the PRV strains Ka, Phylaxia and Dessau, and determined the 3′ end of the gII mRNA by S1 analysis. These data show that the size heterogeneity is caused by the presence of a variable number of tandemly repeated DNA sequence downstream but adjacent to the coding region of the glycoprotein gII gene. The 3′ end of the gII mRNA was mapped about 24 bp upstream of the first repeat unit. A 15 bp sequence 5′ GGGACGGAGGGGAGA 3′ is repeated from three to over 50 times in different 1G fragments. It is the only repeat unit present in strain Ka, whereas the Phylaxia and Dessau strains show additional modifications.