title: Absence of a universal element for tRNAHis identity in Acanthamoeba castellanii.
abstract: The additional G(-1) nucleotide on tRNA(His) is a nearly universal feature that specifies tRNA(His) identity in all three domains of life. In eukaryotes, the G(-1) identity element is obtained by a post-transcriptional pathway, through the unusual 3'-5' polymerase activity of the highly conserved tRNA(His) guanylyltransferase (Thg1) enzyme, and no examples of eukaryotic histidyl-tRNAs that lack this essential element have been identified. Here we report that the eukaryote Acanthamoeba castellanii lacks the G(-1) identity element on its tRNA(His), consistent with the lack of a gene encoding a bona fide Thg1 ortholog in the A. castellanii genome. Moreover, the cytosolic histidyl-tRNA synthetase in A. castellanii exhibits an unusual tRNA substrate specificity, efficiently aminoacylating tRNA(His) regardless of the presence of G(-1). A. castellanii does contain two Thg1-related genes (encoding Thg1-like proteins, TLPs), but the biochemical properties we associate here with these proteins are consistent with a function for these TLPs in separate pathways unrelated to tRNA(His) metabolism, such as mitochondrial tRNA repair during 5'-editing.
authors.affiliation: Department of Chemistry and Biochemistry and Center for RNA Biology, The Ohio State University, Columbus, OH 43210, USA.
authors.forename: Bhalchandra S
authors.initials: BS
authors.lastname: Rao
authors.forename: Fuad
authors.initials: F
authors.lastname: Mohammad
authors.forename: Michael W
authors.initials: MW
authors.lastname: Gray
authors.forename: Jane E
authors.initials: JE
authors.lastname: Jackman
mesh_terms: D048248:Acanthamoeba castellanii / Q000201:enzymology / Q000235:genetics*; D012321:DNA-Directed RNA Polymerases / Q000378:metabolism; D006643:Histidine-tRNA Ligase / Q000378:metabolism; D009713:Nucleotidyltransferases / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D017393:RNA Editing; D000077278:RNA, Mitochondrial; D012343:RNA, Transfer / Q000378:metabolism; D012354:RNA, Transfer, His / Q000737:chemistry* / Q000378:metabolism
chemical_list: D000077278:RNA, Mitochondrial; D012354:RNA, Transfer, His; D012313:RNA; D012343:RNA, Transfer; D009713:Nucleotidyltransferases; C065307:tRNA guanylyltransferase; D012321:DNA-Directed RNA Polymerases; D006643:Histidine-tRNA Ligase