title: Life without post-transcriptional addition of G-1: two alternatives for tRNAHis identity in Eukarya.
abstract: The identity of tRNA(His) is strongly associated with the presence of an additional 5'-guanosine residue (G-1) in all three domains of life. The critical nature of the G-1 residue is underscored by the fact that two entirely distinct mechanisms for its acquisition are observed, with cotranscriptional incorporation observed in Bacteria, while post-transcriptional addition of G-1 occurs in Eukarya. Here, through our investigation of eukaryotes that lack obvious homologs of the post-transcriptional G-1-addition enzyme Thg1, we identify alternative pathways to tRNA(His) identity that controvert these well-established rules. We demonstrate that Trypanosoma brucei, like Acanthamoeba castellanii, lacks the G-1 identity element on tRNA(His) and utilizes a noncanonical G-1-independent histidyl-tRNA synthetase (HisRS). Purified HisRS enzymes from A. castellanii and T. brucei exhibit a mechanism of tRNA(His) recognition that is distinct from canonical G-1-dependent synthetases. Moreover, noncanonical HisRS enzymes genetically complement the loss of THG1 in Saccharomyces cerevisiae, demonstrating the biological relevance of the G-1-independent aminoacylation activity. In contrast, in Caenorhabditis elegans, which is another Thg1-independent eukaryote, the G-1 residue is maintained, but here its acquisition is noncanonical. In this case, the G-1 is encoded and apparently retained after 5' end processing, which has so far only been observed in Bacteria and organelles. Collectively, these observations unearth a widespread and previously unappreciated diversity in eukaryotic tRNA(His) identity mechanisms.
authors.affiliation: Molecular, Cellular and Developmental Biology Program, Center for RNA Biology and Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA.
authors.forename: Bhalchandra S
authors.initials: BS
authors.lastname: Rao
authors.affiliation: Molecular, Cellular and Developmental Biology Program, Center for RNA Biology and Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, USA Jackman.14@osu.edu.
authors.forename: Jane E
authors.initials: JE
authors.lastname: Jackman
mesh_terms: D048248:Acanthamoeba castellanii / Q000201:enzymology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000235:genetics; D006643:Histidine-tRNA Ligase / Q000737:chemistry / Q000502:physiology; D007700:Kinetics; D008969:Molecular Sequence Data; D009713:Nucleotidyltransferases / Q000502:physiology; D010802:Phylogeny; D015800:Protozoan Proteins / Q000737:chemistry / Q000502:physiology; D012323:RNA Processing, Post-Transcriptional; D016053:RNA, Protozoan / Q000096:biosynthesis* / Q000235:genetics; D012354:RNA, Transfer, His / Q000096:biosynthesis* / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics; D046249:Transfer RNA Aminoacylation; D014346:Trypanosoma brucei brucei / Q000201:enzymology*
chemical_list: D015800:Protozoan Proteins; D016053:RNA, Protozoan; D012354:RNA, Transfer, His; D009713:Nucleotidyltransferases; C020842:guanylyltransferase; D006643:Histidine-tRNA Ligase
keywords: G−1 residue; histidyl-tRNA synthetase; tRNA identity; tRNAHis; tRNAHis guanylyltransferase