The selective packaging and annealing of primer tRNALys3 in HIV-1

In HIV-1, tRNA(Lys3) serves as the primer for reverse transcriptase, and during viral assembly, the tRNA(Lys) isoacceptors, tRNA(Lys1,2) and tRNA(Lys3), are selectively packaged into the virion. In this review, we shall first discuss the evidence for the formation of a tRNA(Lys) packaging complex, whose components include Gag, GagPol, genomic RNA, lysyl-tRNA synthetase (LysRS), and tRNA(Lys). Evidence suggests that the formation of this complex involves a Gag/GagPol/viral genomic RNA complex interacting with a tRNA(Lys)/ LysRS complex, with Gag interacting with both GagPol and LysRS, and GagPol interacting with the tRNA(Lys). The interaction of Gag with LysRS is quite specific, does not require the presence of tRNA(Lys), and LysRS is believed to be the target that allows the specific packaging of tRNA(Lys) into the virion. The parameters influencing these interactions, and the molecular sites of interaction, will be discussed. The selective packaging of tRNA(Lys3) into HIV-1 facilitates annealing of tRNA(Lys) to the 5' region of viral RNA genome. This region contains a series of stem loops, and there exists several regions in both the viral RNA and the tRNA(Lys) that are believed to be important for tRNA(Lys) annealing. The annealing is facilitated by viral proteins such as unprocessed Gag, nucleocapsid, and reverse transcriptase.