title: Mitochondrial tRNAs in the lower fungus Spizellomyces punctatus: tRNA editing and UAG 'stop' codons recognized as leucine.
abstract: The mitochondrial DNA of the chytridiomycete fungus Spizellomyces punctatusen codes only eight tRNAs, although a minimal set of 24-25 tRNAs is normally found in fungi. One of these tRNAs has a CAU anticodon and is structurally related to leucine tRNAs, which would permit the translation of the UAG 'stop' codons that occur in most of its protein genes. The predicted structures of all S. punctatus tRNAs have the common feature of containing one to three mis-pairings in the first three positions of their acceptor stems. Such mis-pairing is expected to impair proper folding and processing of tRNAs from their precursors. Five of these eight RNAs were shown to be edited at the RNA level, in the 5'portion of the molecules. These changes include both pyrimidine to purine and A to G substitutions that restore normal pairing in the acceptor stem. Editing was not found at other positions of the tRNAs, or in the mitochondrial mRNAs of S. punctatus. While tRNA editing has not been observed in other fungi, the editing pattern inS.punctatus is virtually identical to that described in the amoeboid protozoan Acanthamoeba castellanii. If this type of mitochondrial tRNA editing has originated from their common ancestor, one has to assume that it was independently lost in plants, animals and in most fungi. Alternatively, editing might have evolved independently, or the genes coding for the components of the editing machinery were laterally transferred.
authors.affiliation: Département de Biochimie, Université de Montréal, CP 6128, succ. Centre Ville, Montréal , Québec H3C 3J7, Canada.
authors.forename: M J
authors.initials: MJ
authors.lastname: Laforest
authors.forename: I
authors.initials: I
authors.lastname: Roewer
authors.forename: B F
authors.initials: BF
authors.lastname: Lang
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D018388:Codon, Terminator; D004271:DNA, Fungal; D004272:DNA, Mitochondrial; D005658:Fungi / Q000145:classification / Q000235:genetics; D007930:Leucine; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D010802:Phylogeny; D012313:RNA; D017393:RNA Editing; D012331:RNA, Fungal; D000077278:RNA, Mitochondrial; D012343:RNA, Transfer; D017386:Sequence Homology, Amino Acid
chemical_list: D018388:Codon, Terminator; D004271:DNA, Fungal; D004272:DNA, Mitochondrial; D012331:RNA, Fungal; D000077278:RNA, Mitochondrial; D012313:RNA; D012343:RNA, Transfer; D007930:Leucine