Structural and functional analyses of the Equine herpesvirus type 1 genomic regions conserved in the defective interfering particles

Equine herpesvirus type 2 (EHV-1) preparations become enriched for defective interfering particles (DIPs) upon serial, undiluted propagation. DIP-rich EHV-1 preparations mediate oncogenic transformation and persistent infection of hamster embryo fibroblasts. Field inversion gel electrophoresis and restriction enzyme analyses demonstrated that the DIP DNA is heterogeneous. The DIP genome is made of subgenomic sequences from the left terminus (0.00 to 0.04 map units) and parts of inverted repeats (Irs) (0.78 to 0.79 and 0.83 to 0.87 map units). Nucleotide sequence analysis of these segments of the IR revealed an origin of replication (ORI) that is nonpalindromic and homologous to the ORI sequences of other herpesviruses. This sequence also contains a short, highly conserved sequence that is the target of DNA binding proteins in cells infected with herpes simplex virus. The ORI sequence is capable of driving the replication of recombinant prokaryotic plasmids in eukaryotic cells. The ORI sequence is precisely conserved in DIP DNA. Two sets of direct repeats located near the ORI may enhance its activity. The analyzed sequences from the IR also code for eight potential open reading frames, including an early gene. These data suggest that the EHV-1 IR codes for the largest number of genes among the IR sequences of...