Nucleotide sequence of acceptor site and termini of integrated avian endogenous provirus ev1: integration creates a 6 bp repeat of host DNA.

The nucleotide sequences at the junctions between host cellular and integrated proviral DNA at the chicken endogenous retrovirus locus ev1 have been determined. These sequences have been compared with that of a DNA fragment presumed to contain the acceptor site for integration of the provirus at this locus. The results show that the integrated ev1 provirus contains a long terminal repeat (LTR) of 273 base pairs (bp). The left and right LTR are identical and contain sequences similar to proposed transcription control signals. In addition, there is a direct repeat of 6 bp of host DNA immediately flanking each provirus terminus. The nucleotide sequence of the fragment that contains the unoccupied acceptor site is identical to that which flanks the ev1 provirus, except that the 6 bp sequence occurs only once. We propose that the repeat was produced during integration by a mechanism similar to that of procaryotic and eucaryotic transposable genetic elements. This and other similarities in structure suggest a common evolution and mode of function for these movable genetic elements.