Branched RNA-linked multicopy single-stranded DNA (msDNA) originally detected in myxobacteria has now been found in a clinical isolate of Escherichia coli. Although lacking homology in the primary structure, the E. coli msDNA is similar in secondary structure to the myxobacterial msDNA's, including the 2′,′5-phosphodiester linkge between RNA and DNA. A chromosomal DNA fragment responsible for the production of msDNA was doned in an E. coli K12 strain; its DNA sequence revealed an open reading frame (ORF) of 586 amino acid residues. The ORF shows sequence similarity with retroviral reverse transcriptases and ribonuclease H. Disrupdon of the ORE blocked msDNA production, indicating that this gene is essential for msDNA synthesis.
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