Structural mechanism of LINE-1 target-primed reverse transcription

Long interspersed element-1 (LINE-1) retrotransposons are the only active autonomous transposable elements in humans. They propagate by reverse transcribing their mRNA into new genomic locations by a process called target-primed reverse transcription (TPRT). Here, we present four cryo-electron microscopy structures of the human LINE-1 TPRT complex, revealing the conformational dynamics of ORF2p and its extensive remodeling of the target DNA for TPRT initiation. We observe nicking of the DNA second strand during reverse transcription of the first strand. Structure prediction identifies high-confidence binding sites for LINE-1-associated factors, namely PCNA and PABPC1, on ORF2p. Together with our structural data, this suggests a mechanism by which these factors regulate retrotransposition and proposes a model for TPRT that accounts for retrotransposition outcomes observed in cells.