A 3' coterminal gene cluster in pseudorabies virus contains herpes simplex virus UL1, UL2, and UL3 gene homologs and a unique UL3.5 open reading frame.

We have determined the nucleotide sequence and transcription pattern of a group of open reading frames of pseudorabies virus (PRV), which are located at the right end of the BamHI-G fragment from 0.664 to 0.695 map units in the unique long region of the genome. Nucleotide sequence analysis revealed four open reading frames. The first three correspond in genome location to the herpes simplex virus type 1 (HSV-1) open reading frames UL1, which codes for glycoprotein L (gL); UL2, which codes for a uracil-DNA glycosylase; and UL3, which codes for a polypeptide of unknown function. The fourth open reading frame, UL3.5, is not present in the HSV-1 genome. Northern (RNA) blot analysis with oligonucleotide and cDNA probes revealed four abundant mRNA species of 3.3, 2.7, 1.8, and 0.9 kb, which are likely to yield polypeptides encoded by the UL1, -2, -3, and -3.5 open reading frames, respectively. All four transcripts were of the early-late kinetic class, transcribed in the same direction, and 3' coterminal. The UL2 and UL3 genes of PRV and HSV-1 have significant amino acid sequence homology, while the UL1 genes are positional homologs and the UL3.5 gene is unique to PRV.