In vitro dimerization of HIV-2 leader RNA in the absence of PuGGAPuA motifs.

Retroviral particles contain a dimeric genome consisting of two full-length, noncovalently linked RNA molecules. Linkage of the two genomes is thought to be critical for a productive reverse transcription reaction and may increase genetic recombination rates. The molecular nature of the dimer linkage structure (DLS) is poorly understood. It was recently shown that in vitro synthesized retroviral transcripts can dimerize in the absence of protein factors. We studied in vitro dimerization of human immunodeficiency virus type 2 (HIV-2) RNA. Specific dimerization of HIV-2 RNAs was observed upon incubation at 37 degrees C in high-salt buffer. Previously, physical and biochemical studies have mapped dimer linkage structures in retroviral leader RNA close to the gag open reading frame. In this study, we found efficient dimerization of HIV-2 RNAs containing only the 5' terminal 255 nucleotides of the leader RNA. Therefore, it seems likely that multiple dimerization signals are present in retroviral leader RNA. The implications for genome dimerization and genome packaging are discussed.