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

Abstract

The primer for initiating reverse transcription in human immunodeficiency virus type 1 (HIV-1) is tRNA^Lys3. Host cell tRNA^Lys is selectively packaged into HIV-1 through a specific interaction between the major tRNA^Lys-binding protein, human lysyl-tRNA synthetase (hLysRS), and the viral proteins Gag and GagPol. Annealing of the tRNA primer onto the complementary primer-binding site (PBS) in viral RNA is mediated by the nucleocapsid domain of Gag. The mechanism by which tRNA^Lys3 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^Lys 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^Lys3 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^Lys to increase the efficiency of tRNA^Lys3 annealing to viral RNA.