Novel endogenous retroviral sequences in the chicken genome closely related to HPRS-103 (subgroup J) avian leukosis virus

HPRS-103, the prototype of avian leukosis virus (ALV) subgroup J, is a rece ntly identified retrovirus associated with myeloid leukosis in meat-type ch ickens. Although this virus shows high sequence identity to other ALV subgr oups within the gag and pol genes, its env gene is highly diverged (with on ly about 40% sequence identity) from other ALV subgroups. On the other hand , the sequence of the env gene of HPRS-103 was 75% identical to that of E51 , a member of the EAV family of endogenous avian retroviruses. It is report ed here that the chicken genome also contains another EAV-related element, EAV-HP, showing much greater sequence identity lover 97%) to the HPRS-103 e nv gene. Southern blotting analysis showed that EAV-HP-related sequences we re distinct from EAV-O and were present in all lines of chicken examined an d in grey jungle fowl, but were absent from several other avian species. Th e potential role of these endogenous sequences in the evolution of ALV subg roup J viruses is discussed.