Characterization of RD114-related endogenous cat retroviral elements ECE2

RD114 virus is an endogenous xenotropic Type C retrovirus of domestic cat. Previously, it had been shown that genomic DNA of cat contained approximately 20 copies of RD114-related sequences. Only one encoded for the replication-competent RD114 virus. The endogenous sequences exhibited substantial sequence conservation within the gag and pol genes and LTRs, but were characterized by deletions and substitutions within the env region. The endogenous cat retroviral element ECE2 was isolated by screening a genomic DNA library of cat liver DNA with an env-specific cDNA of RD114 virus. It contained an env region which differed from all RD114-related sequences so far isolated and was homologous to the corresponding region of replication-competent RD114 with regard to their restriction map and partial sequence analysis (p20). Otherwise, ECE2 had a deletion of approximately 1 kbp in the putative pol gene and, therefore, did not represent the locus of inducible RD114 virus.