Immediate-early gene expression and gene mapping comparisons among isolates of bovine herpesvirus 1 and 5

Bovine herpesviruses (BHV) are associated with a variety of clinical syndromes. Bovine herpesvirus 1 isolates were placed into three genome subtypes based on restriction endonuclease analyses, which were loosely associated by clinical manifestation as BHV1.1 (respiratory), BHV1.2 (genital), and BHV1.3 (encephalitic). More recently the encephalitic isolate has been classified BHV5. A comparison of the cytopathic effect (CPE) in fetal bovine lung cell cultures in the presence of cycloheximide showed that BHV1.1 and 1.2 isolates produced elongated, spindle-shaped CPE, whereas BHV5 produced more syncytial-like CPE. Each BHV-1 subtype synthesized four immediate-early transcripts. The sizes in kb were: 1.6, 3.4, 5.8, 7.5 (BHV1.1); 1.8, 3.6, 5.8, 7.5 (BHV1.2); and 1.8, 3.6, 5.8, 8.6 (BHV5). These transcripts were mapped to the inverted repeat region of each isolate by Southern blot hybridization using cDNA prepared from cycloheximide-treated BHV1-infected cellular polyA RNA. A possible unique immediate-early RNA may be produced by the BHV5 encephalitic isolate from an area of the internal repeat region unique to this isolate. Hybridization analysis using BHV1.1 cloned probes of the immediate-early protein gene, thymidine kinase gene, DNA binding/DNA polymerase gene, and glycoprotein III gene provided information for mapping of these genes to the BHV5 encephalitic isolate.