Structure of the key elements involved in HIV-1 RNA dimerisation. 2a. Secondary structure model of the packaging signal of HIV-1Lai ( ), containing the principal DLS. 2b Proposed sequence of the RNA dimerisation process in HIV-1Lai. The initial kissing hairpin interaction (including loop B) followed by formation of the extended duplex (). 2c. Loop B, one of the critical elements in the dimer interaction. The flexibility of this internal loop allows the duplex to form ().