Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

tRNA splicing is essential in yeast and humans and presumably all eukaryotes. The first two steps of yeast tRNA splicing, excision of the intron by endonuclease and joining of the exons by tRNA ligase, leave a splice junction bearing a 2'-phosphate. Biochemical analysis suggests that removal of this phosphate in yeast is catalyzed by a highly specific 2'-phosphotransferase that transfers the phosphate to NAD to form ADP-ribose 1"-2" cyclic phosphate. 2'-Phosphotransferase catalytic activity is encoded by a single essential gene, TPT1, in the yeast Saccharomyces cerevisiae. We show here that Tpt1 protein is responsible for the dephosphorylation step of tRNA splicing in vivo because, during nonpermissive growth, conditional lethal tpt1 mutants accumulate 2'-phosphorylated tRNAs from eight different tRNA species that are known to be spliced. We show also that several of these tRNAs are undermodified at the splice junction residue, which is always located at the hypermodified position one base 3' of the anticodon. This result is consistent with previous results indicating that modification of the hypermodified position occurs after intron excision in the tRNA processing pathway, and implies that modification normally follows the dephosphorylation step of tRNA splicing in vivo.
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PMID:A conditional lethal yeast phosphotransferase (tpt1) mutant accumulates tRNAs with a 2'-phosphate and an undermodified base at the splice junction. 940 90

tRNA splicing in the yeast Saccharomyces cerevisiae requires an endonuclease to excise the intron, tRNA ligase to join the tRNA half-molecules, and 2'-phosphotransferase to transfer the splice junction 2'-phosphate from ligated tRNA to NAD, producing ADP ribose 1"-2" cyclic phosphate (Appr>p). We show here that functional 2'-phosphotransferases are found throughout eukaryotes, occurring in two widely divergent yeasts (Candida albicans and Schizosaccharomyces pombe), a plant (Arabidopsis thaliana), and mammals (Mus musculus); this finding is consistent with a role for the enzyme, acting in concert with ligase, to splice tRNA or other RNA molecules. Surprisingly, functional 2'-phosphotransferase is found also in the bacterium Escherichia coli, which does not have any known introns of this class, and does not appear to have a ligase that generates junctions with a 2'-phosphate. Analysis of the database shows that likely members of the 2'-phosphotransferase family are found also in one other bacterium (Pseudomonas aeruginosa) and two archaeal species (Archaeoglobus fulgidus and Pyrococcus horikoshii). Phylogenetic analysis reveals no evidence for recent horizontal transfer of the 2'-phosphotransferase into Eubacteria, suggesting that the 2'-phosphotransferase has been present there since close to the time that the three kingdoms diverged. Although 2'-phosphotransferase is not present in all Eubacteria, and a gene disruption experiment demonstrates that the protein is not essential in E. coli, the continued presence of 2'-phosphotransferase in Eubacteria over large evolutionary times argues for an important role for the protein.
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PMID:A functional homolog of a yeast tRNA splicing enzyme is conserved in higher eukaryotes and in Escherichia coli. 982 66

Splicing of precursor tRNAs in plants requires the concerted action of three enzymes: an endonuclease to cleave the intron at the two splice sites, an RNA ligase for joining the resulting tRNA halves and a 2'-phosphotransferase to remove the 2'-phosphate from the splice junction. Pre-tRNA splicing has been demonstrated to occur exclusively in the nucleus of vertebrates and in the cytoplasm of budding yeast cells, respectively. We have investigated the subcellular localization of plant splicing enzymes fused to GFP by their transient expression in Allium epidermal and Vicia guard cells. Our results show that all three classes of splicing enzymes derived from Arabidopsis and Oryza are localized in the nucleus, suggesting that plant pre-tRNA splicing takes place preferentially in the nucleus. Moreover, two of the splicing enzymes, i.e., tRNA ligase and 2'-phosphotransferase, contain chloroplast transit signals at their N-termini and are predominantly targeted to chloroplasts and proplastids, respectively. The putative transit sequences are effective also in the heterologous context fused directly to GFP. Chloroplast genomes do not encode intron-containing tRNA genes of the nuclear type and consequently tRNA ligase and 2'-phosphotransferase are not required for classical pre-tRNA splicing in these organelles but they may play a role in tRNA repair and/or splicing of atypical group II introns. Additionally, 2'-phosphotransferase-GFP fusion protein has been found to be associated with mitochondria, as confirmed by colocalization studies with MitoTracker Red. In vivo analyses with mutated constructs suggest that alternative initiation of translation is one way utilized by tRNA splicing enzymes for differential targeting.
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PMID:Plant pre-tRNA splicing enzymes are targeted to multiple cellular compartments. 1769 77