Characterization of transformation- and replication-specific sequences of reticuloendotheliosis virus

Abstract Using a combination of hybridization and oligonucleotide fingerprinting techniques we have determined the sequence relatedness of oncogenic avian reticuloendotheliosis virus (REV) to its associated helper virus, REV-A, and to the other members of the reticuloendotheliosis (RE) virus group. Our studies have shown that approximately 30% of the genomic sequences of REV are unrelated to the nononcogenic RE viruses. These REV-specific, and presumably oncogenic, sequences are arranged in a contiguous fashion, possibly interrupted by a short stretch of REV-A-related sequences, localized between 1 and 2.7 kilobases (kb) from the 3′-end on the REV genome. We have also identified two regions of REV-A sequences which are deleted in the REV genome. The first region encompasses 3 kb of sequences in the 5′-half of the genome, presumably corresponding to the gag-pol genes. The second region represents 1.5(kb) of the env sequences. These deletions could account for the genetic defectiveness of REV. By studying the sequence relatedness between REV-A and the other RE viruses, we have shown that REV is the only RE virus which contains these oncogenic sequences. We have also determined the relatedness between these viruses. In addition, we have identified a hypervariable region which maps in or near the env gene. The possible significance of this region in accounting for both the varied pathogenicity of the RE viruses and the origin of oncogenic REV is discussed.