Mechanism for the chimeras' formation by LINE enzymatic machinery. (Step 1) LINE pre-integration complex binds LINE, SINE or RNA in the cytoplasm. (Step 2) The resulting ribonucleoprotein is transferred to the nucleus. (Step 3) Reverse transcription of the bound RNA primed by a genomic DNA single-stranded break (target site primed reverse transcription). (Step 4A) Successful integration of the reverse transcribed cDNA copy into the genomic DNA. (Step 4B) Switch of templates on another RNA during the reverse transcription. (Step 5A) Integration of the chimera formed into genomic DNA. (Step 5B) The second template switch to another RNA with subsequent DNA reparation mediates formation of a tripartite chimeric retrogene insertion flanked by short direct repeats. The normal LINE integration pathway is: steps (1) – (2) – (3) – (4A).