A 4.8 kilobase segment located at the left-terminal in the unique long (UL) region of infectious laryngotracheitis virus (ILTV) SA-2 strain contained three open reading frames (ORFs). The first of 421 amino acids (aa) was located at map units 0.065 to 0.07, and its predicted 48 kiloDaltons (kDa) protein product has significant homology to the immediate early regulatory protein ICP27 (UL54) of herpes simplex virus type-1 (HSV-1), to varicella-zoster virus (VZV) ORF4 and to equine herpesvirus 1 (EHV-1) ORF5. The zinc finger conserved in the C-terminal of the proteins from HSV-1, VZV and EHV-1, is poorly conserved in ILTV homologue. The second ORF of 336 aa, located at map units 0.075 to 0.08, has a predicted molecular weight (MW) of 38 kDa with significant homology to glycoprotein K (gK) of HSV-1 (UL53), ORF5 of VZV and ORF6 of EHV-1. ILTV gK has features characteristic of a membrane-bound glycoprotein. The 3' region of a third ORF was located at map units 0.08 to 0.095. Translation of the sequence revealed significant homology to the 3'-region of the DNA helicase-primase complex protein (UL52) of HSV-1, ORF6 of VZV and ORF 7 of EHV-1. Northern blot analyses were used to characterize the ILTV ICP27, gK and DNA helicase mRNAs. The data revealed that ILTV ICP27 is an immediate early gene that encodes a 1.6 kb mRNA, ILTV gK encodes a late transcript of 1.8 kb, while ILTV DNA helicase encodes a late transcript of 3.7 kb.