Further characterization of the gapped DNA intermediates of human spumavirus: evidence for a dual initiation of plus-strand DNA synthesis.

We recently reported the presence of linear duplex DNA intermediates with a gap in the middle of the molecules in the replicative cycle of human (HSRV) and simian (SFV1) spumaviruses. The polypurine tract (PPT), at the 5' boundary of the 3' long terminal repeat, was found to be duplicated in the gap region. By molecular analysis of HSRV proviral DNA with region- and strand-specific probes, we have now determined that the gap is located on plus-strand DNA and that it is 120 bases long with the 3' end mapping at the duplicated PPT site. Kinetic analysis of proviral DNA provided evidence that the gap did not result from processing of a complete, full-length DNA molecule. These data strongly suggest that plus-strand DNA synthesis is initiated at both PPT sites.