FIG. 5.

Model for production of small, 17-bp deletions by SIV IN and IN associated with nonionic-detergent-lysed HIV-1 virions. The LTR donors are shown as U5 and U3 donor substrates (light lines). The 3′-OH termini of two donors are inserted into the target (dark lines), resulting in free 3′-OH target ends. Note that the inserted donor termini must be pointing in opposite directions on the target DNA to produce a deletion. For full-site integration resulting in a 5-bp host site duplication, the donor termini must be pointing toward each other. The 17-bp spacing is located on the target DNA that is occupied by a minimal-size protein structure whose number of IN subunits is unknown. The two thin arrows indicate nicking events by IN or a nonspecific nuclease. The resulting structure is indicated at the bottom. Either full-site integration or the formation of the indicated deletion by IN will produce linear 3.8-kbp donor-target recombinants.