Organization and function of the ORIs sequence in the genome of EHV-1 DI particles.

Equine herpesvirus type 1 (EHV-1) cultures enriched for defective interfering particles (DIP) mediate oncogenic transformation and persistent infection in permissive hamster embryo fibroblasts. We have recently demonstrated that an origin of replication (ORI) is located within the central portion (map units 0.828 and 0.948) of the inverted repeat sequence (IRs) of the short region of the standard EHV-1 genome. In the generation of the genome of EHV-1 DI particles, sequences from this internal portion of the IRs recombine with sequences at the long region terminus at nucleotides 3244-3251. In this paper we report that the ORIs sequence is precisely conserved in the DIP genome, that direct repeat sequences near the ORIs sequence which may enhance DNA replication are mutated in the DIP genome, and that the ORI sequence of DIP DNA is functional in DNA replication assays.