Association of a chicken repetitive element with the endogenous virus-21 slow-feathering locus

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.