msDNA-Ec48, the smallest multicopy single-stranded DNA from Escherichia coli.

Previously we have reported a novel bacterial reverse transcriptase (RT) from Escherichia coli ECOR58 strains in which the YXDD box was replaced with LVDD (J.-R. Mao, S. Inouye, and M. Inouye, Biochem. Biophys. Res. Commun. 227:489-493, 1996). Here we determined the structure of the multicopy single-stranded DNA (msDNA) produced by the RT. The msDNA was found to consist of a single-stranded DNA of 48 nucleotides in length, the shortest msDNA thus far identified from natural sources. The msDNA, the RT, and the retron are designated msDNA-Ec48, RT-Ec48, and retron-Ec48, respectively. On the basis of the structure of the msr gene, the RNA molecule of msDNA-Ec48 is predicted to be composed of 119 ribonucleotides; it is the longest RNA among the known msDNAs. Analysis of the DNA sequences flanking the retron indicates that retron-Ec48 is associated with a prophage related to phages P2 and P4.