English: Proposed mechanism for the synthesis of msDNA. (A) Folding of the primer-template RNA into a secondary structure allows the 2'-OH group of a specific branching G residue to serve as a primer to initiate cDNA synthesis by the retron reverse transcriptase. (B) Synthesis of cDNA is accompanied by RNaseH digestion of the template strand. (C) In the completed msDNA molecule, part of the RNA template remains joined to the 5' end of the cDNA.