DNA sequence and transcriptional analysis of the UL1 to UL5 gene cluster of infectious laryngotracheitis virus.

We have cloned and sequenced the KpnI L and M restriction fragments of infectious laryngotracheitis virus (ILTV, gallid herpesvirus 1) DNA, which are localized adjacently at the right end of the unique long region of the genome. Within the 6930 bp DNA sequence six complete open reading frames (ORFs) were identified. The predicted amino acid sequences of four of them exhibit significant homologies to the UL5 (helicase), UL4, UL3 and UL2 (uracil-DNA glycosylase) genes, which are conserved in similar arrangement in all alphaherpesvirus genomes characterized up to now. A short ORF of 72 codons between UL3 and UL4 of ILTV is positionally homologous to the UL3.5 gene present in the genomes of different members of the Varicellovirus genus of alphaherpesviruses, but not in herpes simplex virus. The predicted ILTV protein encoded upstream of UL2 possesses limited sequence homology to the UL1 gene product of herpesviruses, the structural glycoprotein L. The presence of a N-terminal signal sequence, a conserved N-glycosylation site and two conserved cysteine residues indicates a similar function of the putative ILTV protein. Upstream of the UL1 gene of ILTV the C-terminal part of an additional ORF designated as ULO was identified, which exhibits no significant homology to known herpesvirus genes. RNA analyses indicate the expression of all detected ILTV genes including ULO.