Reverse transcription is a central event in the retroviral life cycle, allowing the RNA genome being reverse-transcribed into DNA by the viral reverse transcriptase enzyme. In murine leukemia virus (MLV), we showed that (Miller et al., Nature 2014) the reverse transcriptase enzyme initiates from a highly specific RNA-RNA complex, which is formed between a primer molecule, a specific tRNA packaged into the virion from the host cell during virus assembly, and a region at the 5' end of genomic RNA called the U5 Primer Binding Site (U5-PBS). The residues essential for primer annealing are initially locked in intramolecular interactions; hence, annealing requires the chaperone activity of the retroviral nucleocapsid (NC) protein to facilitate structural rearrangements.