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Proc Natl Acad Sci U S A. 1990 Dec;87(23):9454-8.

Retron for the 67-base multicopy single-stranded DNA from Escherichia coli: a potential transposable element encoding both reverse transcriptase and Dam methylase functions.

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  • 1Department of Biochemistry, Robert Wood Johnson Medical School, Rutgers, University of Medicine and Dentistry of New Jersey, Piscataway 08854.


The region (retron-Ec67) required for the biosynthesis of a branched-RNA-linked multicopy single-stranded DNA (msDNA-Ec67) from a clinical isolate of Escherichia coli was mapped at a position equivalent to 19 min on the K-12 chromosome. The element containing the retron consisted of a unique 34-kilobase sequence that was flanked by direct repeats of a 26-base-pair sequence found in the K-12 chromosomal DNA. This suggests that the 34-kilobase element was probably integrated into the E. coli genome by a mechanism related to transposition or phage integration. In the 34-kilobase sequence an open reading frame of 285 residues was found, which displays 44% sequence identity with the E. coli Dam methylase. Interestingly, there are three GATC sequences, the site of Dam methylation, in the promoter region of the gene for reverse transcriptase.

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