EXPRESSION OF AN EQUINE HERPESVIRUS-1 ICP22 ICP27 HYBRID PROTEIN ENCODED BY DEFECTIVE INTERFERING PARTICLES ASSOCIATED WITH PERSISTENT INFECTION/

Defective interfering (DI) particles of equine herpesvirus type 1 (EHV -1) are capable of mediating persistent infection (S. A. Dauenhauer, R . A. Robinson, and D. J. O'Callaghan, J. Gen, Virol, 60:1-14, 1982; R. A. Robinson, R. B. Vance, and D. J. O'Callaghan, J. Virol, 36:204-219 , 1980), Sequence analysis of cloned DI particle DNA revealed that por tions of two regulatory genes, ICP22 (IR4) and ICP27 (UL3), are linked in frame to form a unique hybrid open reading frame (ORF), This hybri d ORF, designated as the IR4/UL3 gene, encodes the amino-terminal 196 amino acids of the IR4 protein (ICP22 homolog) and the carboxy-termina l 68 amino acids of the UL3 protein (ICP27 homolog), Portions of DNA s equences encoding these two regulatory proteins, separated by more tha n 115 kbp in the standard virus genome, were linked presumably by a ho mologous recombination event between two identical 8-bp sequences, Rev erse transcriptase-PCR and S1 nuclease analyses revealed that this uni que ORF is transcribed by utilizing the transcription initiation site of ICP22 and the polyadenylation signal of ICP27 in DI particle enrich ed infection, Immunoprecipitation and Western blot (immunoblot) analys es with antisera to the ICP22 and ICP27 proteins demonstrated that a 3 1-kDa hybrid protein was synthesized in the DI particle-enriched infec tion but not in standard virus infection, This 31-kDa hybrid protein w as expressed at the same time as the ICP22 protein in DI particle-enri ched infection and migrated at the same location on polyacrylamide gel electrophoresis as the protein expressed from a cloned IR4/UL3 expres sion vector, These observations suggested that the unique IR4/UL3 hybr id gene is expressed from the DI particle genome and may play a role i n DI particle-mediated persistent infection.