Molecular mimicry of human tRNA anti-codon domain by HIV-1 RNA genome facilitates tRNA primer annealing

The primer for initiating reverse transcription in human immunodeficiency virus type 1 (HIV-1) is tRNA. Host cell tRNA is selectively packaged into HIV-1 through a specific interaction between the major tRNA-binding protein, human lysyl-tRNA synthetase (hLysRS), and the viral proteins Gag and GagPol. Annealing of the tRNA primer onto the complementary primerbinding site (PBS) in viral RNA is mediated by the nucleocapsid domain of Gag. The mechanism by which tRNA is targeted to the PBS and released from hLysRS prior to annealing is unknown. Here, we show that hLysRS specifically binds to a tRNA anti-codon-like element (TLE) in the HIV-1 genome, which mimics the anti-codon loop of tRNA and is located proximal to the PBS. Mutation of the U-rich sequence within the TLE attenuates binding of hLysRS in vitro and reduces the amount of annealed tRNA in virions. Thus, LysRS binds specifically to the TLE, which is part of a larger LysRS binding domain in the viral RNA that includes elements of the Psi packaging signal. Our results suggest that HIV-1 uses molecular mimicry of the anti-codon of tRNA to increase the efficiency of tRNA annealing to viral RNA.