Molecular analysis of several classes of endogenous feline leukemia virus elements.

Five recombinant DNA clones of endogenous feline leukemia virus-related DNA sequences were isolated by screening a lambda phage genomic library of cat placental DNA with a probe specific to the gag-pol region of infectious feline leukemia virus. The clones containing retroviral long terminal repeat-like sequences demonstrated the existence of different size classes of endogenous elements in the cat genome, including those of nearly full length in which the gag region is heterogeneous but all of pol and most of env are highly conserved. Other size classes included elements with major deletions in gag or pol. A genomic DNA analysis suggested that the majority of endogenous elements were close to full length in size and that the highly truncated sequences which we described previously (Soe et al., J. Virol. 46:829-840, 1983) represented only a subset of the elements present. A restriction analysis of genomic DNA suggested a high degree of conservation in pol and the 5' portion of env among the various endogenous sequences present in the cat genome. We also found by using DNA transfection that while all of the endogenous clones were noninfectious, there was differential expression of the elements which we examined. These findings correlate with the subgenomic expression of endogenous feline leukemia virus sequences in cat placental tissue.