Gene organization in herpesvirus of turkeys: identification of a novel open reading frame in the long unique region and a truncated homologue of pp38 in the internal repeat.

The DNA sequence of a 4.792-kb fragment comprising 3.176 kb of the long unique region (UL) and 1.605 kb of the internal repeat (IRL) flanking UL of herpesvirus of turkeys (HVT) was determined. Three potential open reading frames (ORFs) and an origin of replication have been identified. ORF 1, which maps entirely within UL, has the capacity to code for an 82K protein, 731 amino acids long, which has a counterpart in Marek's disease virus (MDV) but not in other herpesviruses. ORF 2 has the potential to encode a protein consisting of 129 amino acids with a predicted M(r) of 13.5K which appears to be unique to HVT. ORF 3 is encoded entirely within IRL and codes for an 84 amino acids long protein with a predicted M(r) of 8.5K. ORF 3 shows significant homology with the C-terminal region of the MDV-1-specific phosphoprotein pp38 and its recently identified homologue in MDV-2. Northern blot analysis of RNA extracted from HVT-infected chick embryo fibroblasts identified a 5.6-kb RNA transcribed in a leftward direction toward UL scanning ORF 1, ORF 2, and ORF 3 and a 2.8-kb also transcribed leftward toward UL which spanned only ORFs 2 and 3. In addition, a 2.3- to 2.8-kb RNA family was transcribed rightwards through the origin of replication. In vitro transcription and translation of ORF 1 and ORF 3 resulted in the synthesis of polypeptides consistent with their expected M(r), but ORF 2 failed to produce any translation product.