HPRS-103 (EXOGENOUS AVIAN-LEUKOSIS VIRUS, SUBGROUP-J) HAS AN ENV GENE-RELATED TO THOSE OF ENDOGENOUS ELEMENTS EAV-0 AND E51 AND AN E-ELEMENT FOUND PREVIOUSLY ONLY IN SARCOMA-VIRUSES

The avian leukosis and sarcoma virus (ALSV) group comprises eight subg roups based on envelope properties. HPRS-103, an exogenous retrovirus recently isolated from meat-type chicken lines, is similar to the viru ses of these subgroups in group antigen but differs from them in envel ope properties and has been assigned to a new subgroup, J. HPRS-103 ha s a wide host range in birds, and unlike other nontransforming ALSVs w hich cause late-onset B-cell lymphomas, HPRS-103 causes late-onset mye locytomas. Analysis of the sequence of an infectious clone of the comp lete proviral genome indicates that HPRS-103 is a multiple recombinant of at least five ALSV sequences and one EAV (endogenous avian retrovi ral) sequence. The HPRS-103 env is most closely related to the env gen e of the defective EAV-E51 but divergent from those of other ALSV subg roups, Probing of restriction digests of line 0 chicken genomic DNA ha s identified a novel group of endogenous sequences (EAV-HP) homologous to that of the HPRS-103 env gene but different from sequences homolog ous to EAV and E51. Unlike other replication-competent nontransforming ALSVs, HPRS-103 has an E element in its 3' noncoding region, as found in many transforming ALSVs. A deletion found in the HPRS-103 U3 EFII enhancer factor-binding site is also found in all replication-defectiv e transforming ALSVs (including MC29, which causes rapid-onset myelocy tomas).