  We previously proposed the existence of DNA to DNA transcription in
eukaryotic cells, but the mechanism by which single-stranded DNA (ssDNA)
transcript is produced and released from the genome remains unknown. We once
speculated that the mechanism of DNA to DNA transcription might be similar to
that of DNA to RNA transcription, but now we propose that endonuclease
dependent transcript cutout may be a possible mechanism of DNA to DNA
transcription, in which a copy of ssDNA fragment (transcript) between two nicks
produced by nicking endonuclease is released from double-stranded DNA (dsDNA)
region in the genome by an unknown ssDNA fragment releasing enzyme. The gap in
the dsDNA will be filled through DNA repair mechanism. Occasionally, multiple
copies of ssDNA transcripts could be produced through multiple rounds of
cutout-repair-cutout cycle.
