Multicopy single-stranded DNA (msDNA) is a type of extrachromosomal satellite DNA that consists of a single-stranded DNA molecule covalently linked via a 2-5phosphodiester 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.