The kissing hairpin sequence promotes recombination within the HIV-I 5' leader region.

The role of RNA-RNA template interactions in facilitating recombination during reverse transcription of minus strand DNA has been examined. The tested hypothesis is that template switching by reverse transcriptase is promoted at sites where homologous regions of two RNAs are brought in close proximity via stable intertemplate interactions. Frequency and distribution of template switching between homologous donor and acceptor RNAs were examined within the human immunodeficiency virus type I (HIV-I) 5'-untranslated region (UTR) containing the dimer initiation sequence (DIS). Results were compared with control nondimerizing templates from the pol region. The dimerizing UTR templates displayed a 4-fold higher transfer efficiency than the control. A striking 53% of transfers in the UTR mapped near the DIS, of which two-thirds occurred immediately 5' to this sequence. In the UTR template, deletion of the DIS hairpin disrupted template dimerization and caused a 4-fold drop in transfer efficiency. Insertion of the DIS within the pol template increased both dimerization and transfer efficiency. Transfer distributions revealed that in both sets of templates, DIS-induced dimerization increased the efficiency of transfers across the whole template, with the transfers peaking around the dimerization site. Overall, these results suggest that template dimerization facilitated by the unique geometry of the DIS-promoted kissing interactions effectively promotes recombination within the HIV-I 5'-UTR.