title: tRNA evolution from the proto-tRNA minihelix world.
abstract: Multiple models have been advanced for the evolution of cloverleaf tRNA. Here, the conserved archaeal tRNA core (75-nt) is posited to have evolved from ligation of three proto-tRNA minihelices (31-nt) and two-symmetrical 9-nt deletions within joined acceptor stems (93 - 18 = 75-nt). The primary evidence for this conclusion is that the 5-nt stem 7-nt anticodon loop and the 5-nt stem 7-nt T loop are structurally homologous and related by coding sequence. We posit that the D loop was generated from a third minihelix (31-nt) in which the stem and loop became rearranged after 9-nt acceptor stem deletions and cloverleaf folding. The most 3´-5-nt segment of the D loop and the 5-nt V loop are apparent remnants of the joined acceptor stems (14 - 9 = 5-nt). Before refolding in the tRNA cloverleaf, we posit that the 3'-5-nt segment of the D loop and the 5-nt V loop were paired, and, in the tRNA cloverleaf, frequent pairing of positions 29 (D loop) and 47 (V loop) remains (numbered on a 75-nt tRNA cloverleaf core). Amazingly, after >3.5 billion years of evolutionary pressure on the tRNA cloverleaf structure, a model can be constructed that convincingly describes the genesis of 75/75-nt conserved archaeal tRNA core positions. Judging from the tRNA structure, cloverleaf tRNA appears to represent at least a second-generation scheme (and possibly a third-generation scheme) that replaced a robust 31-nt minihelix protein-coding system, evidence for which is preserved in the cloverleaf structure. Understanding tRNA evolution provides insights into ribosome and rRNA evolution.
authors.affiliation: a Department of Physiology , Michigan State University , E. Lansing , MI , USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Root-Bernstein
authors.affiliation: b Troy High School , Troy , MI , USA.
authors.forename: Yunsoo
authors.initials: Y
authors.lastname: Kim
authors.affiliation: b Troy High School , Troy , MI , USA.
authors.forename: Adithya
authors.initials: A
authors.lastname: Sanjay
authors.affiliation: c Department of Biochemistry and Molecular Biology , Michigan State University , E. Lansing , MI , USA.
authors.forename: Zachary F
authors.initials: ZF
authors.lastname: Burton
mesh_terms: D001105:Archaea / Q000235:genetics*; D019143:Evolution, Molecular; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D019642:RNA, Archaeal / Q000737:chemistry / Q000235:genetics; D012343:RNA, Transfer / Q000737:chemistry* / Q000235:genetics*
chemical_list: D019642:RNA, Archaeal; D012343:RNA, Transfer
keywords: D loop; T loop; V loop; acceptor stems; anticodon loop; proto-tRNA minihelices; rRNA evolution; ribosome evolution; tRNA evolution; tRNA microhelices; tRNA structure