How is msDNA stored in E. coli?
The msDNA-retron system was first discovered in M. xanthus soil bacteria, which have an average 500-700 copies of this DNA. (1) msDNA is encoded by a single-locus retron integrated into the bacterial chromosome by some mechanism of phage integration or transposition (2). Thus retrons are highly diverse in their chromosomal localization and size. Among the 7 msDNAs in E. coli, retrons are integrated at various locations, and vary in size from 1.3 kb to 3.0 kb (2). After transcription of the chromosomal retron, encoded msDNA exists free of the chromosome in the cell cytoplasm, and can be isolated by the same methods used to isolate plasmids (1). msDNA isolated from E. coli exists as a large complex, composed of one molecule of msDNA and several units of the reverse transcriptase.
(1) Lampson, B.C, Inouye S, Inouye M. (1991). msDNA of bacteria. Prog. Nucleic Acid Res. Mol. Biol. 40: 1–24.
(2) Yamanaka K, Shimamoto T, Inouye S, Inouye M. Retrons. In: Mobile DNA II. Craig NL, Craigie R, Gellert M, Lambowitz AM, eds. (2002). Washington, DC: ASM Press. 784–95.
-- Olivia H. 15 May 2009 2:34 EDT