| Equine herpesvirus type 1 (EHV-1) can establish a cytolytic infection in a variety of cell types and, in the presence of EHV-1 defective interfering particles (DIPs), can establish a persistent infection in conjunction with cellular transformation. To understand, in part, the molecular aspects and viral regulatory mechanisms that determine the outcome of EHV-1 infection, transcripts originating from an essential regulatory region (immediate-early (IE) gene; IR1) on the EHV-1 genome were characterized and mapped by northern hybridization, S1 nuclease, and primer extension analyses. These experiments demonstrated that: (1) EHV-1 synthesizes a spliced, 6.0 kb IE mRNA species that maps completely within each inverted repeat (IR) segment, (2) a 372 base intron is spliced from the leader region of the IE mRNA (major IE open reading frame (ORF) = 1,487 amino acids), (3) an early (E) gene (IR2) is embedded completely within the IE gene and encodes a 4.4 kb mRNA species that is 3;EHV-1 DI particles are generated following serial, undiluted propagation of EHV-1, and their genome is derived from three segments of the standard genome, including; the L-terminus (m.u. 0.00-0.023), the junction of the unique long (UL) and IR sequences (mu. 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). In EHV-1 persistently infected cells (DI cells), the pattern of transcription from the IE gene region is altered as compared to that observed in cytolytic infection. A 2.2 kb RNA species, unique to the DI cells, maps in close proximity (UL/IRs junction) to the 3... |
