Figure 5
Model for how palindromic sequences in the PBS could promote spatial proximity between the genomic RNA displaced during the synthesis of + sssDNA and the + sssDNA itself. In the scheme, regions that harbour chevrons in the opposite orientation (inverted repeats) can anneal. Panel A, PBS annealed to the tRNA 3′ end (genomic RNA in blue, tRNA in green). Panel B, formation of + sssDNA after copying the cPBS component of the tRNA, displacement of the genomic RNA and the degradation of the tRNA (indicated by shading). Once the tRNA degraded, the (+) DNA PBS and the genomic RNA PBS can either form intramolecular hairpins (panel C) or a RNA/DNA heteroduplex (panel C’). Panel D, RNA sequence of the PBS (isolate MAL) with indicated the palindromic sequences involved in the formation of the stem of a hairpin according to Isel and colleagues26, given as an example for the possible presence of palindromic sequences in the PBS.
