Sequence alignment of the vhs coding regions. The vhs sequences of HSV-1, HSV-2, and PRV were analysed by DNA Star MegaAlign software. Identical residues are denoted as “.” and deleted amino acids are indicate as “-”. Four conserved region, designated as Boxes I–IV (reported in Berthomme et al. ) are marked. In addition, several deduced residues, numbered according to the PrV vhs gene, that have been reported as being responsible for ribonuclease activities are indicated with arrowheads.