Reverse transcriptase from Escherichia coli exists as a complex with msDNA and is able to synthesize double-stranded DNA.
Reverse transcriptase required for the synthesis of msDNA.Ec67 in an Escherichia coli strain was purified as a large molecular weight complex with msDNA. The complex sedimented in a glycerol gradient at an s value greater than 19. The predominant protein species co-purifying with reverse transcriptase activity in the complex had a molecular weight estimated at 65,000 which is close to the expected size of 67,227 for the Ec67-reverse transcriptase. In addition, the large complex also contained msDNA.Ec67. The purified complex was able to synthesize cDNA using 5 S rRNA as a template (annealed to a synthetic DNA primer), and a double-stranded DNA using a synthetic DNA template (annealed to a synthetic DNA primer). When msDNA.Ec67 was used as a natural template:primer, the purified complex produced two major products: a 103-base single-stranded DNA by extending the 3' end of msDNA using msdRNA as a template, and a 60-base double-stranded DNA product resulting from the converse reaction in which the 3' end of msdRNA is extended using msDNA as a template. The results suggest that bacterial reverse transcriptase is capable of producing single-stranded cDNA and possibly double-stranded DNA as well. Possible implications of these findings on the biology of the msDNA-retron system are discussed.