LONG CELLULAR REPEATS FLANKING A DEFECTIVE HTLV-I PROVIRUS - IMPLICATION FOR SITE-TARGETED INTEGRATION

Retroviruses generally integrate as proviruses which are flanked by lo ng-terminal repeats (LTRs) on both 5' and 3' ends. Since these LTRs ar e required for the efficient integration mediated by the viral integra se, it is believed that defective proviruses with a single LTR are nor mally formed by deletion after integration. However, we found no delet ion of cellular sequences around the integration site of such a defect ive HTLV-1. Rather, we identified 99 bp-long direct repeats adjacent t o both ends of the defective provirus. The repeated cellular sequences contained a potential poly(A) signal followed by a retroviral primer- binding-site-like sequence. The presence of the direct repeats of cell ular sequences can be explained by the integration of the defective vi rus through homologous recombination between cellular and viral read-t hrough sequences.