We characterized the gene encoding the pseudorabies virus (PrV) homologue of the herpes simplex virus 1 UL12 open reading frame that encodes the alkaline nuclease. The deduced PrV UL12 product was 492 amino acid residues and exhibited three conserved regions among herpesviruses. Northern blot analysis indicated that three transcripts (3.2, 1.6 and 1 kb) were encoded in this region and the UL12 corresponds to the 1.6-kb transcript. Primer extension and UL12-specific cDNA cloning were performed to verify the precise location of the UL12 transcript. These data indicated that the transcription start site of UL12 was located at 47–62 nucleotides upstream of the UL12 translation start site and the polyadenylation cleavage site was located at 15 or 16 nucleotides downstream the typical polyadenylation signal. Furthermore, the 53-kDa UL12 product, which indeed has deoxyribonuclease activity, was evidenced by in vitro expression.
