Localization of HTLV-1 and HIV-1 proviral sequences in chromosomes of persistently infected cells

Integration sites for HTLV-1 and HIV-1 proviruses were detected by FISH on the chromosomes of HTHIV27 cells persistently infected by HIV-1 (strain III B). HTLV-1 signals were found on 9 loci of chromosomes 4, 6, 9, 15 and 16. Integration sites of GC-rich HTLV-1 provirus are located in GC-rich isochor es, confirming an 'isopycnic' integration, namely an integration in which t he GC level of the host sequences around the integration site match the GC level of the provirus. This conclusion is not only derived from the composi tional map of human chromosomes, but also from HTLV-1 hybridization on comp ositional fractions of human DNA. Integration of GC-poor HIV-1 provirus was found on 4 loci of chromosomes 2, 7, 17 and 19. One copy of a complete HIV -1 provirus, which is active, was integrated in H1 isochores, whereas other defective copies were located in GC-poor L isochores. These results are di scussed in terms of regional integration of retroviral sequences.