Transcriptional analysis of the UL1 gene of equine herpesvirus 1: a gene conserved in the genome of defective interfering particles.

Defective interfering particles (DIPs) of equine herpesvirus type 1 (EHV-1) are biologically active, in that they mediate the coestablishment of oncogenic transformation and persistent infection in permissive, primary hamster embryo fibroblasts. The DIP genome is composed of EHV-1 sequences originating from the L-terminus (mapping units (m.u.) 0.00-0.023), the junction of the unique long (UL) region and the internal inverted repeat (IR) (m.u. 0.78-0.79 and 0.99-1.00), and the central portion of the IR (m. u. 0.83-0.87 and 0.91-0.95). The nature of one of the genes (UL1) mapping at the L-terminus was analyzed at the RNA level by Northern blot hybridization and S1 nuclease analyses. These data, and DNA sequencing analyses reported previously revealed that the UL1 gene: (1) contains a major open reading frame (ORF) of 258 amino acids, (2) is a homologue of the ORF2 gene of varicella zoster virus (VZV), (3) is conserved in the genome of DIPs of EHV-1, (4) encodes a 1.2-kb early (E) mRNA that is transcribed toward the short region of the genome, (5) utilizes a transcription initiation site approximately 1,120 nucleotides from the L-terminus, and (6) utilizes a transcription termination site approximately 2211 nucleotides from the L-terminus. These initial studies serve as the basis of future work to determine the function of the UL1 gene in cytolytic infection, and its potential role in EHV-1 persistent infection.