title: Emergence of a dual-catalytic RNA with metal-specific cleavage and ligase activities: the spandrels of RNA evolution.
abstract: In vitro selection, or directed molecular evolution, allows the isolation and amplification of rare sequences that satisfy a functional-selection criterion. This technique can be used to isolate novel ribozymes (RNA enzymes) from large pools of random sequences. We used in vitro evolution to select a ribozyme that catalyzes a novel template-directed RNA ligation that requires surprisingly few nucleotides for catalytic activity. With the exception of two nucleotides, most of the ribozyme contributes to a template, suggesting that it is a general prebiotic ligase. More surprisingly, the catalytic core built from randomized sequences actually contains a 7-nt manganese-dependent self-cleavage motif originally discovered in the Tetrahymena group I intron. Further experiments revealed that we have selected a dual-catalytic RNA from random sequences: the RNA promotes both cleavage at one site and ligation at another site, suggesting two conformations surrounding at least one divalent metal ion-binding site. Together, these results imply that similar catalytic RNA motifs can arise under fairly simple conditions and that multiple catalytic structures, including bifunctional ligases, can evolve from very small preexisting parts. By breaking apart and joining different RNA strands, such ribozymes could have led to the production of longer and more complex RNA polymers in prebiotic evolution.
authors.affiliation: Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA. lfl@princeton.edu
authors.forename: L F
authors.initials: LF
authors.lastname: Landweber
authors.forename: I D
authors.initials: ID
authors.lastname: Pokrovskaya
mesh_terms: D000818:Animals; D001483:Base Sequence; D002413:Cations, Divalent / Q000494:pharmacology; D019020:Directed Molecular Evolution; D007438:Introns / Q000235:genetics; D008345:Manganese / Q000494:pharmacology; D008969:Molecular Sequence Data; D009843:Oligoribonucleotides; D017354:Point Mutation; D011118:Polynucleotide Ligases / Q000235:genetics / Q000378:metabolism; D016337:RNA, Catalytic / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment; D013768:Tetrahymena / Q000235:genetics; D014500:Uracil Nucleotides; D058727:RNA, Small Untranslated
chemical_list: D002413:Cations, Divalent; D009843:Oligoribonucleotides; D016337:RNA, Catalytic; D014500:Uracil Nucleotides; D008345:Manganese; D011118:Polynucleotide Ligases; D058727:RNA, Small Untranslated