title: Highly specific recognition of primer RNA structures for 2'-OH priming reaction by bacterial reverse transcriptases.
abstract: A minor population of Escherichia coli contains retro-elements called retrons, which encode reverse transcriptases (RT) to synthesize peculiar satellite DNAs called multicopy single-stranded DNA (msDNA). These RTs recognize specific RNA structures in their individual primer-template RNAs to initiate cDNA synthesis from the 2'-OH group of a specific internal G residue (branching G residue). The resulting products (msDNA) consist of RNA and single-stranded DNA, sharing hardly any sequence homology. Here, we investigated how RT-Ec86 recognizes the specific RNA structure in its primer-template RNA. On the basis of structural comparison with HIV-1 RT, domain exchanges were carried out between two E. coli RTs, RT-Ec86 and RT-Ec73. RT-Ec86 (320 residues) and RT-Ec73 (316 residues) share only 71 identical residues (22%). From the analysis of 10 such constructs, the C-terminal 91-residue sequence of RT-Ec86 was found to be essential for the recognition of the unique stem-loop structure and the branching G residue in the primer-template RNA for retron-Ec86. Using the SELEX (systematic evolution of ligands by exponential enrichment) method with RT-Ec86 and primer RNAs containing random sequences, the identical stem-loop structure (including the 3-U loop) to that found in the retron-Ec86 primer-template RNA was enriched. In addition, the highly conserved 4-base sequence (UAGC), including the branching G residue, was also enriched. These results indicate that the highly diverse C-terminal region recognizes specific stem-loop structures and the branching G residue located upstream of the stem-loop structure. The present results with seemingly primitive RNA-dependent DNA polymerases provide insight into the mechanisms for specific protein RNA recognition.
authors.affiliation: Department of Biochemistry, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.
authors.forename: S
authors.initials: S
authors.lastname: Inouye
authors.forename: M Y
authors.initials: MY
authors.lastname: Hsu
authors.forename: A
authors.initials: A
authors.lastname: Xu
authors.forename: M
authors.initials: M
authors.lastname: Inouye
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004277:DNA, Single-Stranded; D019020:Directed Molecular Evolution; D004926:Escherichia coli / Q000201:enzymology*; D054303:HIV Reverse Transcriptase / Q000235:genetics / Q000378:metabolism; D008024:Ligands; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D012313:RNA / Q000737:chemistry / Q000378:metabolism*; D012329:RNA, Bacterial / Q000737:chemistry / Q000378:metabolism*; D012194:RNA-Directed DNA Polymerase / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D018626:Retroelements; D013379:Substrate Specificity
chemical_list: D004277:DNA, Single-Stranded; D008024:Ligands; C034477:RNA primers; D012329:RNA, Bacterial; D011993:Recombinant Fusion Proteins; D018626:Retroelements; C058681:msDNA; D012313:RNA; D054303:HIV Reverse Transcriptase; D012194:RNA-Directed DNA Polymerase