Reverse transcriptase-dependent synthesis of a covalently linked, branched DNA-RNA compound in E. coli B

Association of a retroelement with a P4-like cryptic prophage (retronphage phi R73) integrated into the selenocystyl tRNA gene of Escherichia coli

“…2. As found in all the other retrons so far characterized (retron-Mx162 [8,21], retron-Sal63 (11,12), retron-Ec67 [31], retron-Ec86 [34], and retron-Mx65 [22]), a sequence immediately upstream of the msDNA sequence (al in Fig. 2) was repeated in inverted orientation downstream of the msDNA sequence (a2) as shown in Fig.…”

“…Thus, these retrons probably derived from a common ancestral bacterium exist-ing before the divergence of these two myxobacterial species. In contrast, only approximately 10% of natural isolates of Escherichia coli so .far examined contain msDNA, and their primary structures are completely different from each other (19,31,34). Furthermore, the primary sequences and domain structures of E. coli RTs are substantially different from each other (31,34).…”

“…In contrast, only approximately 10% of natural isolates of Escherichia coli so .far examined contain msDNA, and their primary structures are completely different from each other (19,31,34). Furthermore, the primary sequences and domain structures of E. coli RTs are substantially different from each other (31,34). Thus, it has been proposed that retrons were acquired from other systems late in the evolution of E. coli (19).…”

“…Recently, we have shown that P2 phage can act as a helper to excise the cryptic prophage and to package its genome into an infectious virion. The newly formed phage (retronphage 4R73) can also lysogenize a new host strain, reintegrating its genome into the selC gene and enabling the newly formed lysogen to produce msDNA-Ec73 (S. Inouye The recent discovery of reverse transcriptase (RT) in bacteria raises intriguing questions concerning its origin and functions (22,23,31,34). Although bacterial RTs are highly diverged from each other at the level of primary amino acid sequences (approximately 50o identity) and domain structure, they share conserved sequences with retroviral RTs, indicating that they are evolutionarily related (9,23,52).…”

Discovery of an insertion sequence, IS116, from Streptomyces clavuligerus and its relatedness to other transposable elements from actinomycetes

“…3). Comparison with the recently discovered reverse transcriptases of Gram-negative bacteria reinforces these tentative alignments (Lampson et al, 1989;Inouye et al, 1989;Lim & Maas, 1989). Thus, although these sequence comparisons do not imply that some or all of these actinomycete elements use reverse transcription during their transposition, it seems plausible that their principal gene products may have some properties in common with reverse transcriptases.…”