Levin, I., U.S. Department of Agriculture, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823.
Smith, E.J., U.S. Department of Agriculture, Avian Disease and Oncology Laboratory, East Lansing, Michigan 48823.

The DNA sequences of an endogenous virus ev21-cell junction fragment (JFIL-1), and the pristine ev21 unoccupied region were analyzed. Comparisons of 3' proviral sequences of JFIL-1 with comparable regions of ev2, the prototype Rous-associated provirus (RAV-0), revealed minor single-base substitutions in the transmembrane domain of proviral envelope glycoprotein and the long terminal repeat of ev21. In the cell component of the JFIL-1, insertion of a 9-bp direct repeat and deletion of a guanine deoxynucleotide abolished HaeIII and BalI recognition sites that were present in the pristine region. Upstream from the insertion site, a large region was 71 and 75% homologous with dispersed chicken repetitive (CR1) elements associated with vitellogenin and very low density apolipoprotein II genes, respectively. Southern blot hybridizations and comparisons of CR1 motifs such as polypurine tracts, a tandem imperfect octamer, and 6-bp duplications indicated that this sex-linked, CR1 element (CR1ev21) may be the longest member of this family reported thus far.