Multicopy single-stranded DNA
（重定向自Multicopy single stranded DNA）
![msDNA from Stigmatella aurantiaca compared with msDNA from the closely related Myxococcus xanthus. The hypervariable domain in the DNA sequence is shaded gray. The highly conserved AGC RNA sequence including the branch G is shaded pink. An RNA cleavage site between precursor and product forms of msDNA is indicated by a red triangle. Redrawn from Dhundale et al.[1]](/uploads/202501/28/Myxobacterial_msDNA.svg1122.png)
![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 RNase H 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.[10]](/uploads/202501/28/Msdna_synthesis1122.png)
Multicopy single-stranded DNA (msDNA) is a type of extrachromosomal satellite DNA that consists of a single-stranded DNA molecule covalently linked via a 2'-5'phosphodiester bond to an internal guanosine of an RNA molecule. The resultant DNA/RNA chimera possesses two stem-loops joined by a branch similar to the branches found in RNA splicing intermediates. The coding region for msDNA, called a "retron", also encodes a type of reverse transcriptase, which is essential for msDNA synthesis.