FIG 2 .
Schematic representation of the reverse transcription process of the 3′-PPT mutant leading to the 1-LTR circle formation. The first reverse transcription steps of the 3′-PPT mutant (steps 1 to 3) are similar to the WT. In step 4, we hypothesize that the entire RNA sequence, including the mutated PPT, is degraded by RNase H and that the initiation of the +DNA synthesis (step 5) occurs from sequences located upstream of the 3′ PPT. Once the partial +DNA is synthesized and the RNase H has cleaved the tRNALys (step 6), the partially double-stranded DNA can be circularized by pairing the PBS sequences located on both sides of the DNA, which leads to the formation of 1-LTR circles.