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PubMed1991

Chromosomal assignment of a large tRNA gene cluster (tRNA(Leu), tRNA(Gln), tRNA(Lys), tRNA(Arg), tRNA(Gly)) to 17p13.1.

A cluster of tRNA genes (tRNA(UAGLeu), tRNA(CUGGln), tRNA(UUULys), tRNA(UCUArg)) and an adjacent tRNA(GCCGly) have been assigned to human chromosome 17p12-p13.1 by in situ hybridization using a 4.2 kb human DNA fragment for tRNA(Leu), tRNA(Gln), tRNA(Lys), tRNA(Arg), and, for tRNA(Gly), 1.3 kb and 0.58 kb human DNA fragments containing these genes as probes. This localization was confirmed and refined to 17p13.100-p13.105 using a somatic cell hybrid mapping panel. Preliminary experiments with the biotinylated tRNA Leu, Gln, Lys, Arg probe and metaphase spreads from other great apes suggest the presence of a hybridization site on the long arm of gorilla (Gorilla gorilla) chromosome 19 and the short arm of orangutan (Pongo pygmaeus) chromosome 19 providing further support for homology between HSA17, GGO19 and PPY19.

Animals↗

PubMed1990

Genes for tRNA(Gly), tRNA(His), tRNA(Lys), tRNA(Phe), tRNA(Ser) and tRNA(Tyr) are encoded in Oenothera mitochondrial DNA.

The genes coding for tRNA(Gly), tRNA(His), tRNA(Lys), tRNA(Phe), tRNA(Ser) and tRNA(Tyr) have been identified in Oenothera mitochondrial DNA. Sequence analysis of these genes and their surrounding sequences are presented and compared with other known tRNA genes from plant mitochondria. All six deduced tRNA sequences can be folded into the classical cloverleaf structure model. Only the tRNA(His) gene shows high homology with the corresponding chloroplast gene and thus appears to be derived from a transfer event of chloroplast sequences into the mitochondrial genome. The sequences surrounding this gene, however, show little similarity with the chloroplast genome. The other five deduced tRNAs display a much lower similarity with their chloroplast counterparts and thus appear to be genuine mitochondrial tRNAs. These tRNAs are highly conserved between monocots and dicots with maximally three nucleotides differing between the Oenothera sequences and their wheat homologues. A purine-rich sequence is found upstream of each tRNA gene in Oenothera, similar to wheat mitochondrial tRNA genes, that could be involved in transcription signalling.

Base Sequence↗

PubMed1992

The first human genes for tRNA(ArgICG), tRNA(GlyUCC), and tRNA(ThrIGU) and more tRNA(Val) pseudogenes: expression and pre-tRNA maturation in HeLa cell-free extracts.

A functional tRNA(Val) gene, which codes for the major tRNA(ValIAC) isoacceptor species, and three new tRNA(Val) pseudogenes have been isolated from human genomic DNA. Two tRNA(Val) pseudogenes and a tRNA(Val) variant gene were found to be associated with tRNA genes encoding tRNA(ArgICG), tRNA(GlyUCC), and tRNA(ThrIGU), respectively, on distinct DNA fragments. All tRNA genes, including the pseudogenes, are actively transcribed in HeLa nuclear extract. Pre-tRNAs of tRNA(Val), tRNA(Arg), tRNA(Thr), and tRNA(Gly) genes are correctly processed to mature-sized tRNAs, whereas the three tRNA(Val) pseudogenes yield stable pre-tRNAs in vitro. These findings reveal that, together with the three known pseudogenes, half of the members of the human tRNA(Val) gene family are pseudogenes, all of which are active in homologous nuclear extracts in vitro and presumably also in vivo.

Base Sequence↗

PubMed1977

Hydrolytic action of aminoacyl-tRNA synthetases from baker's yeast. "Chemical proofreading" of Thr-tRNA Val by valyl-tRNA synthetase studied with modified tRNA Val and amino acid analogues.

The properties of native and of two modified tRNA Val species in the correction of misactivated threonine by valyl-tRNA synthetase have been studied. Whereas Thr-tRNA Val-C-C-A could not be isolated in the valyl-tRNA synthetase catalyzed reaction, Thr-tRNA Val-C-C-3'dA is isolable in up to 50% yield in this system and tRNA Val-C-C-3'NH2A is fully aminoacylated with threonine by the same enzyme. The hydrolysis of preformed Thr-tRNA Val-C-C-A by free valyl-tRNA synthetase is 30 times faster than the corresponding breakdown of Val-tRNA Val-C-C-A. This hydrolytic activity is also observed with Thr-tRNA Val-C-C-3'dA although the rate is reduce to that of the reaction of Val-tRNA Val-C-C-A. Modification of the threonine to O-methylthreonine, which is also a substrate for valyl-tRNA synthetase, leads to stabilization of the O-methylthreonyl-tRNA esters. The AMP/PP independent hydrolysis under aminoacylating conditions, which is a measure of the correction process, indicates that O-MeThr-tRNA Val-C-C-A is only very slowly corrected while the tRNA Val-C-C-3'dA and tRNA Val-C-C-3'NH2A esters are completely stable. Removal of the methoxy group of O-methylthreonine as in alpha-amino-butyric acid increases the rate of the hydrolytic reaction and once again alpha-Abu-tRNA Val-C-C-A and alpha-Abu-tRNA Val-C-C-3'dA are unstable under aminoacylating conditions and not isolable.

Amino Acyl-tRNA Synthetases↗

PubMed1975

The plant aminoacyl-tRNA synthetases. Purification and characterization of valyl-tRNA, tryptophanyl-tRNA and seryl-tRNA synthetases from yellow-lupin seeds.

Valyl-tRNA, tryptophanyl-tRNA, and seryl-tRNA synthetases from yellow lupin seeds Lupinus luteus were purified to homogeneity by ammonium sulfate fractionation, hydrophobic chromatography on aminohexyl-Sepharose column and affinity chromatography on tRNA-Sepharose column. Valyl-tRNA synthetase consists of one polypeptide chain of molecular weight 125000 as judged by Sephadex G-200 gel filtration and dodecylsulfate-polyacrylamide gel electrophoresis in the presence of reducing agent. Seryl-tRNA synthetase, Mr equals 110000, is composed of two 55000-Mr subunits. Tryptophanyl-tRNA synthetase exhibits molecular weight of 200000 on Sephadex G-200 and 37000 in dodecylsulfate-polyacrylamide gel electrophoresis. This indicates that tryptophanyl-tRNA synthetase consists of several subunits (probably four). Since the seryl-tRNA synthetase exhibits the same mobility on dodecylsulfate-polyacrylamide gels both in the presence and absence of reducing agent it is concluded that there is no covalent bond(s) between the subunits of the enzyme. There is also no covalent bond(s) between the subunits of tryptophanyl-tRNA synthetase. Effect of anti-sulfhydryl reagents, monovalent salts, pH and different buffers on activity of the three synthetases is described. Kinetic constants for the substrates of the synthetases are also given. dATP is a substrate for seryl-tRNA synthetase but not for valyl-tRNA and tryptophanyl-tRNA synthetases.

Amino Acyl-tRNA Synthetases↗

PubMed1980

Phenylalanyl-tRNA, lysyl-tRNA, isoleucyl-tRNA and arginyl-tRNA synthetases. Substrate specificity in the ATP/PPi exchange with regard to ATP analogs.

The analogs of ATP have been tested in the ATP/PPi exchange reaction of phenylalanyl-tRNA, lysyl-tRNA, isoleucyl-tRNA and arginyl-tRNA synthetases from baker's yeast. Three compounds are substrates for phenylalanyl-tRNA, seven for lysyl-tRNA, two for isoleucyl-tRNA and five for arginyl-tRNA synthetase. Their Km and V values have been determined. No analog was an inhibitor. (3'-dATP), 3'-Deoxyadenosine 5'-triphosphate which is an inhibitor of the four enzymes in the aminoacylation reaction, becomes a good substrate in the PPi exchange. Additionally lysyl-tRNA synthetase accepts two analogs with modifications at position 6 of the purine and three analogs modified at the ribose moiety as substrates in the PPi exchange, whereas these compounds are inactive or inhibitors in the aminoacylation reaction. In general the enzymes are less specific in the ATP/PPi exchange and the results indicate a more sophisticated proof of the nucleotide moiety upon aminoacylation. This could occur with the aminoacyladenylate intermediate as well as with any other intermediate.

Adenosine Triphosphate↗

PubMed1990

Structure and expression of tomato mitochondrial genes coding for tRNA(Cys) (GCA), tRNA(Asn) (GUU) and tRNA(Tyr) (GUA): a native tRNA(Cys) gene is present in dicot plants but absent in monocot plants.

The nucleotide sequences of tRNA(Asn) (GUU) and tRNA(Tyr) (GUA) genes from tomato mitochondria and their flanking regions have been determined. The tomato mitochondrial tRNA(Asn) gene is located 2.1 kb downstream from the tRNA(Cys) gene reported previously (Izuchi and Sugita 1989) and shows a nearly complete identity with the corresponding chloroplast gene. The tRNA(Tyr) gene, which shows only 73% homology with the corresponding chloroplast gene, has to be considered a "native" mitochondrial tRNA gene and is 535 bp from the "chloroplast-like" tRNA(Asn) gene on the same strand. Northern hybridization analysis revealed that the three tRNA genes are transcribed in tomato mitochondria. Southern hybridization analysis of tomato, sugar beet. rice and wheat mitochondrial DNAs, with oligonucleotide probes for mitochondrial or chloroplast tRNA genes, demonstrated that the mitochondrial tRNA(Cys) gene found in tomato is present in dicot plants but not in monocots. On the other hand, a chloroplast-like tRNA(Cys) gene exists in monocot plants.

Base Sequence↗

PubMed1992

Hyperprocessing of tRNA by the catalytic RNA of RNase P. Cleavage of a natural tRNA within the mature tRNA sequence and evidence for an altered conformation of the substrate tRNA.

In the transposon copia-related retrovirus-like particles of Drosophila, a 39-nucleotide-long fragment from the 5'-region of Drosophila initiator methionine tRNA (tRNA(iMet)) is used as the primer for copia minus-strand reverse transcription. This primer tRNA(iMet) fragment is thought to be produced by cleavage within the mature tRNA(iMet) sequence. We call this cleavage hyperprocessing. We have previously reported that catalytic RNA of RNase P from Escherichia coli (M1RNA) cleaves the synthetic tRNA(iMet) precursor in vitro at several sites within the mature tRNA sequence. Based on this result, we proposed a model for formation of the primer tRNA fragment involving RNase P. Here we show that natural tRNA(iMet) prepared from Drosophila adult flies can be cleaved by M1RNA. Using mutant tRNA(iMet) substrates, we also show that these cleavages are dependent on the occurrence of an altered conformation of the tRNA substrate. This is evidence that a tRNA can exist in aqueous solution at least in part in an altered conformation.

Animals↗

PubMed1982

Nucleotide sequences of yeast genes for tRNA(2), tRNA(2) and tRNA(1): homology blocks occur in the vicinity of different tRNA genes.

Three members of a collection of pBR322-yeast DNA recombinant plasmids containing yeast tRNA genes have been analyzed and sequenced. Each plasmid carries a single tRNA gene: pY44, tRNA(2); pY41, tRNA(2); pY7, tRNA(1). All three genes are intronless and terminate in a cluster of Ts in the non-coding strand. The sequence information here and previously determined sequences allow an extensive comparison of the regions flanking several yeast tRNA genes. This analysis has revealed novel features in tRNA gene arrangement. Blocks of homology in the flanking regions were found between the tRNA genes of an isoacceptor family but, more interestingly, also between genes coding for tRNAs of different amino-acid specificities. Particularly, three examples are discussed in which sequence elements in the neighborhood of different tRNA genes have been conserved to a high degree and over long distances.

Journal Article↗

PubMed1993

Degradation of the arginyl-tRNA synthetase protein during purification by affinity chromatography on immobilized total tRNA and immobilized tRNA, specific for arginyl-tRNA synthetase.

Arginyl-tRNA synthetase was prepared from Bom:NMRI mouse liver postribosomal supernatants. Purification was performed by either gel filtration on Sephadex G-200 or chromatofocusing before affinity chromatography on immobilized total tRNA (mixture of tRNA's, specific for all aminoacyl-tRNA synthetases), followed by affinity chromatography on immobilized tRNA, specific for arginyl-tRNA synthetase. The purification factor for arginyl-tRNA synthetase activity was 16700x. Following sodium dodecyl sulphate polyacrylamide electrophoresis several protein bands were found in the purified material. All these protein bands were shown to possess arginyl-tRNA synthetase activity.

Amino Acyl-tRNA Synthetases↗

PubMed1979

Studies on tRNA adaptation, tRNA turnover, precursor tRNA and tRNA gene distribution in Bombyx mori by using two-dimensional polyacrylamide gel electrophoresis.

Eighteen out of twenty amino acids have been used for identifying tRNAs from the silkworm Bombyx mori L. fractionated on two-dimensional polyacrylamide gel electrophoresis. 43 spots out of 53 have been identified. This mapping confirms previous results and brings new answers to some questions on the regulation of tRNA biosynthesis. 1. In addition to quantitative adaptation of tRNAs to the composition of silk proteins (fibroin from the posterior silk gland, sericin from the middle part) and of iso-tRNAs from posterior silk gland to the major codons of fibroin mRNA, we also observe adaptation of tRNA from various tissues to the average amino acid content of proteins from fat body, gut, gonads and carcass of the silkworm. 2. In the silk gland, turnover rates of several tRNA species are similar. The selective accumulation of tRNAs needed for decoding fibroin and sericin mRNAs which takes place during the Vth larval instar, cannot be explained by the occurrence of a preferential degradation of some tRNA species. 3. Under given conditions for incubating silk glands, it is possible to obtain an accumulation of precursor tRNA species, which are enriched in pre-tRNAAla and pre-tRNAGly in the posterior silk gland and pre-tRNASer in the middle part. 4. The distribution of tRNA genes is not random. tRNA genes for glycine, alanine and serine are prominent. Selective transcription of batteries of iso-tRNA genes could explain our data.

Animals↗

PubMed1998

Minimal tRNA(Ser) and tRNA(Sec) substrates for human seryl-tRNA synthetase: contribution of tRNA domains to serylation and tertiary structure.

The recognition process of tRNA(Ser) and tRNA(Sec) by human seryl-tRNA synthetase (SerRS) was studied using T7 transcripts representing defined regions of human tRNA(Ser) or tRNA(Sec) and the influence of the tRNA elements on serylation and tertiary structure was elucidated. The anticodon arms of both tRNAs showed no contribution to serylation in contrast to the acceptor stems and the long extra arms. D and T arms were only involved in formation of the L-shaped tRNA structure, not in the recognition process between tRNAs and SerRS. This is the first report of microhelices adapted from human tRNAs being aminoacylated by their homologous synthetase.

Anticodon↗

PubMed1977

The plant aminoacyl-tRNA synthetases. Effect of sodium chloride on tRNA aminoacylation and aminoacyl-tRNA decomposition catalysed by aminoacyl-tRNA synthetases from yellow lupin seeds.

The initial velocity and the extent of aminoacylation are affected by sodium chloride in the lupin aminoacylation systems involving serine, isoleucine, lysine, leucine, phenylalanine and valine. Pyrophosphorolysis and enzymatic hydrolysis of [14C]Val-tRNA catalysed by lupin valyl-tRNA synthetase are inhibited by sodium chloride nearly to the same extent. Evidence is presented that when a limiting amount of synthetase is used, the equilibrium of the aminoacylation reaction in the lupin valine system is determined only by the rate of aminoacylation and non-enzymatic deacylation of aminoacyl-tRNA, the former but not the latter reaction being dependent on concentration of the enzyme and monovalent salt.

Amino Acyl-tRNA Synthetases↗

PubMed1995

Nucleotides of tRNA (Glu) involved in recognition by barley chloroplast glutamyl-tRNA synthetase and glutamyl-tRNA reductase.

The biosynthesis of delta-aminolevulinate (ALA), via the C-5 pathway, requires tRNA(Glu) as a cofactor for the glutamyl tRNA(Glu) synthetase and the glutamyl tRNA(Glu) reductase which are the first two enzymes in this three step pathway. These two enzymes form a ternary complex with the tRNA(Glu) in Chlamydomonas reinhardtii suggesting that the recognition elements on the tRNA cofactor are different for each enzyme. Chemical modification and comparative studies with tRNA(Glu)s from a number of species were used to determine the nucleotides involved in the recognition of the barley chloroplast tRNA(Glu) by the barley enzymes. The barley chloroplast tRNA(Glu) is chemically modified both before and after ligation to glutamate with monobromobimane or CNBr. The chemically modified tRNA(Glu) is a poor substrate for the glutamyl-tRNA synthetase and the chemically modified glutamyl-tRNA(Glu) is used as a substrate for glutamyl-tRNA(Glu) reductase. The tRNA(Glu) from the chloroplasts if barley, Chlamydomonas reinhardtii, tobacco, cucumber, wheat and spinach and tRNA(Glu) from Synechocystis PCC6803, Escherichia coli, barley germ and bakers yeast and the barley chloroplast tRNA(Gln) are all effective substrates for the barley chloroplast glutamyl-tRNA synthetase. A comparison of the sequences of these tRNAs shows 19 conserved bases and five of these bases, G10, A26, U34, U35 and A37 are suggested as recognition elements of barley glutamyl tRNA(Glu) synthetase by assuming a similar binding orientation as in the crystal structure of the E. coli tRNA(Gln) GlnRS complex. The glutamyl-tRNA(Glu) from E. coli, bakers yeast and barley germ and the barley chloroplast glutamyl-tRNA(Gln) are not effective substrates for the barley chloroplast glutamyl-tRNA(Glu) reductase. A comparison of the sequences of these four tRNA species with the sequences of the tRNA(Glu) species that can be used as substrate by the glutamyl-tRNA(Glu) reductase yields seven common differences in the primary sequence. These 7 nucleotides, A7-U66, U29-A41, A53-U61, and U72 are expected to be required for recognition by the barley chloroplast glutamyl-tRNA(Glu) reductase.

Aldehyde Oxidoreductases↗

PubMed1988

Tertiary structure of Escherichia coli tRNA(3Thr) in solution and interaction of this tRNA with the cognate threonyl-tRNA synthetase.

The solution structure of Escherichia coli tRNA(3Thr) (anticodon GGU) and the residues of this tRNA in contact with the alpha 2 dimeric threonyl-tRNA synthetase were studied by chemical and enzymatic footprinting experiments. Alkylation of phosphodiester bonds by ethylnitrosourea and of N-7 positions in guanosines and N-3 positions in cytidines by dimethyl sulphate as well as carbethoxylation of N-7 positions in adenosines by diethyl pyrocarbonate were conducted on different conformers of tRNA(3Thr). The enzymatic structural probes were nuclease S1 and the cobra venom ribonuclease. Results will be compared to those of three other tRNAs, tRNA(Asp), tRNA(Phe) and tRNA(Trp), already mapped with these probes. The reactivity of phosphates towards ethylnitrosourea of the unfolded tRNA was compared to that of the native molecule. The alkylation pattern of tRNA(3Thr) shows some similarities to that of yeast tRNA(Phe) and mammalian tRNA(Trp), especially in the D-arm (positions 19 and 24) and with tRNA(Trp), at position 50, the junction between the variable region and the T-stem. In the T-loop, tRNA(3Thr), similarly to the three other tRNAs, shows protections against alkylation at phosphates 59 and 60. However, tRNA(3Thr) is unique as far as very strong protections are also found for phosphates 55 to 58 in the T-loop. Compared with yeast tRNA(Asp), the main differences in reactivity concern phosphates 19, 24 and 50. Mapping of bases with dimethyl sulphate and diethyl pyrocarbonate reveal conformational similarities with yeast tRNA(Phe). A striking conformational feature of tRNA(3Thr) is found in the 3'-side of its anticodon stem, where G40, surrounded by two G residues, is alkylated under native conditions, in contrast to other G residues in stem regions of tRNAs which are unreactive when sandwiched between two purines. This data is indicative of a perturbed helical conformation in the anticodon stem at the level of the 30-40 base pairs. Footprinting experiments, with chemical and enzymatic probes, on the tRNA complexed with its cognate threonyl-tRNA synthetase indicate significant protections in the anticodon stem and loop region, in the extra-loop, and in the amino acid accepting region. The involvement of the anticodon of tRNA(3Thr) in the recognition process with threonyl-tRNA synthetase was demonstrated by nuclease S1 mapping and by the protection of G34 and G35 against alkylation by dimethyl sulphate. These data are discussed in the light of the tRNA/synthetase recognition problem and of the structural and functional properties of the tRNA-like structure present in the operator region of the thrS mRNA.

Affinity Labels↗

PubMed2005

Glu-Q-tRNA(Asp) synthetase coded by the yadB gene, a new paralog of aminoacyl-tRNA synthetase that glutamylates tRNA(Asp) anticodon.

Analysis of the completed genome sequences revealed presence in various bacteria of an open reading frame (ORF) encoding a polypeptide chain presenting important similarities with the catalytic domain of glutamyl-tRNA synthetases but deprived of the C-terminal anticodon-binding domain. This paralog of glutamyl-tRNA synthetases, the YadB protein, activates glutamate in the absence of tRNA and transfers the activated glutamate not on tRNA(Glu) but instead on tRNA(Asp). It has been shown that tRNA(Asp) is able to accept two amino acids: aspartate charged by aspartyl-tRNA synthetase and glutamate charged by YadB. The functional properties of YadB contrast with those of the canonical glutamyl-tRNA synthetases, which activate Glu only in presence of the cognate tRNA before aminoacylation of the 3'-end of tRNA. Biochemical approaches and mass spectrometry investigations revealed that YadB transfers the activated glutamate on the cyclopenthene-diol ring of the modified nucleoside queuosine posttranscriptionally inserted at the wobble position of the anticodon-loop to form glutamyl-queuosine. Unstability of the ester bond between the glutamate residue and the cyclopenthene-diol (half-life 7.5 min) explains why until now this modification escaped detection. Among Escherichia coli tRNAs containing queuosine in the wobble position, only tRNA(Asp) is substrate of YadB. Sequence comparison reveals a structural mimicry between the anticodon-stem and loop of tRNA(Asp) and the amino acid acceptor-stem of tRNA(Glu). YadB, renamed glutamyl-Q-tRNA(Asp) synthetase, constitutes the first enzyme structurally related to aminoacyl-tRNA synthetases which catalyzes a hypermodification in tRNA, and whose function seems to be conserved among prokaryotes. The discovery of glutamyl-Q-tRNA(Asp) synthetase breaks down the current paradigm according to which the catalytic domain of aminoacyl-tRNA synthetases recognizes the amino acid acceptor-stem of tRNA and aminoacylates the 3'-terminal ribose. The evolutionary significance of the existence of an aminoacyl-tRNA synthetase paralog dedicated to the hypermodification of a tRNA anticodon will be discussed.

Amino Acid Sequence↗

PubMed1996

The discriminator bases G73 in human tRNA(Ser) and A73 in tRNA(Leu) have significantly different roles in the recognition of aminoacyl-tRNA synthetases.

The recognition of human tRNA(Leu) or tRNA(Ser) by cognate aminoacyl- tRNA synthetases has distinct requirements. Only one base change (A73-->G) in tRNA(Leu) is required to generate an efficient serine acceptor in vitro, whereas several changes in three structural domains (the acceptor stem, DHU loop and long extra arm) of tRNA(Ser) are necessary in order to produce a leucine acceptor. Hence, the molecular basis for the discrimination between human tRNA(Ser) and tRNA(Leu) by the seryl-tRNA synthetase depends almost exclusively on a highly specific recognition of the discriminator base G73. In order to elucidate the specific role of the functional groups of this base in discrimination, tRNA(Ser) constructs were made which contain the artificial base analogues 2-aminopurine riboside or inosine at the discriminator position 73. Aminoacylation of these constructs by a HeLa S100 extract showed that molecules with 2-aminopurine riboside, but not with inosine, in position 73 could be serylated at low efficiency. However, the 2-aminopurine riboside and the inosine derivatives of tRNA(Ser) were equally efficient competitive inhibitors of serylation, whereas tRNAs(Ser) with any other natural base at position 73 did not competitively inhibit serylation of tRNA(Ser). This was in contrast to leucylation of tRNA(Leu), where tRNA(Leu) transcripts with any other nucleotide in the discriminator position acted as strong competitive inhibitors. These results suggest that the discriminator bases in human tRNA(Ser) and tRNA(Leu) play completely different roles in recognition of the tRNAs by their cognate aminoacyl-tRNA synthetases.

Amino Acyl-tRNA Synthetases↗

PubMed2005

Evolution from possible primitive tRNA-viroids to early poly-tRNA-derived mRNAs: a new approach from the poly-tRNA theory.

Poly-tRNA theory have revealed that the tRNA gene-clusters in the Bacillus subtilis trrnD- and rrnB-operons are relics of early peptide-synthesizing RNA apparatus. The trrnD-type and rrnB-type poly-tRNA models were re-analyzed by using recent databases. The results elucidated that the 16 amino acid (aa)-trrnD- and the 21 aa-rrnB-peptides (whose aa sequences are in the order of aa specificities of tRNAs in the respective tRNA cluster) are really relics of earliest peptides encoded by most primitive mRNAs, trrnD-mRNA and rrnB-mRNA, which are homologous to tRNA(Gly) and tRNA(His), respectively. Genes encoding various protein superfamilies (including pgtB protein, glycyl-tRNA synthetase alpha, C-type lectin, F1-ATP-synthase gamma, etc) were concluded to have derived from tRNA(Gly)-tRNA(Cys)-tRNA(Leu) region (including trrnD-mRNA region) in the trrnD-poly-tRNA. Genes for another group of protein superfamilies (including adenylate kinase, glyceraldehyde-3-phosphate dehydrogenase, helix-turn-helix DNA-binding domains, etc.) were found to have derived rrnB-mRNA, which is most plausibly homologous to a region containing the tRNA(His) of the rrnB-poly-tRNA. Thus Proto-tRNA((Gly)) reconstructed from tRNA(Gly) and other tRNAs strongly suggested that proto-tRNA was most plausibly a viroid-like possibly self-cleavable replicable ribozyme possessing a possible hammerhead-like structure.

Amino Acid Sequence↗