CHARACTERIZATION OF NUCLEAR TRNA(TYR) INTRONS - THEIR EVOLUTION FROM RED ALGAE TO HIGHER-PLANTS

We have previously isolated numerous intron-containing nuclear tRNA(Ty r) genes derived from either monocatyledonous (Triticum) or dicotyledo nous (Arabidopsis, Nicotiana) plants by screening the corresponding ge nomic phage libraries with a synthetic tRNA(Tyr)-specific oligonucleot ide, Here we have characterized additional tRNA(Tyr) genes from phylog enetically divergent plant species representing red algae (Champia),br own algae (Cystophyllum), green algae (Ulva), stonewort (Chara), liver wort (Marchantia), moss (Polytrichum), fern (Rumohra) and gymnosperms (Ginkgo) using amplification of the coding sequences from the correspo nding genomic DNAs by polymerase chain reaction (PCR), All novel tRNA( Tyr) genes contain intervening sequences of variable sequence and leng th ranging in size from 11 to 21 bp, However, two features are conserv ed in all plant pre-tRNA(Tyr) introns: they possess a uridine and less frequently an adenosine at the 5' boundary and can adopt similar intr on secondary structures in which an extended anticodon helix of 4-5 bp is formed by base-pairing between nucleotides of the intron and the a nticodon loop, In order to elucidate the potential role of the highly conserved uridine at the first intron position, we have replaced it by all other nucleosides in an Arabidopsis pre-tRNA(Tyr) and have studie d in wheat germ extract its effect on splicing and on conversion of U to Psi in the G Psi A anticodon, Furthermore, we discuss the putative acquisition of tRNA(Tyr) introns at an early step of evolution after t he separation of Archaea and Eucarya. (C) 1997 Federation of European Biochemical Societies.