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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effect of biologically inactive and active tRNA conformers on heat inactivation of leucyl-tRNA synthetase was investigated. The data presented show that inactive tRNA conformers seem to form complexes with leucyl-tRNA synthetase, but the thermal stability of the enzyme involved in the complex with inactive and active tRNA conformers is rather different.
Mol Biol (Mosk)
PMID:[Characteristic features of heat inactivation of leucyl-tRNA- synthetase from the rabbit liver in the presence of various tRNA conformers]. 656 5

We have studied leucine transport in several Chinese hamster-human hybrid cell lines obtained by fusion of a temperature-sensitive line of Chinese hamster ovary cells, ts025C1, and normal human leukocytes. A hybrid cell line exhibiting a twofold increase in L-leucine uptake over that in the parental cell line was found. This hybrid cell line, 158CnpT-1, was temperature resistant, whereas the parental Chinese hamster ovary mutant, ts025C1, contained a temperature-sensitive leucyl-tRNA synthetase mutation. An examination of the different amino acid transport systems in this hybrid cell line revealed a specific increase of system L activity with no significant changes in systems A and ASC. The Vmax for L-leucine uptake exhibited by the hybrid 158CnpT-1 was twice that in the CHO parental mutant, ts025C1. Cytogenetic analysis showed that the hybrid 158CnpT-1 contains four complete human chromosomes (numbers 4, 5, 10, and 21) and three interspecific chromosomal translocations in a total complement of 34 chromosomes. Biochemical and cytogenetic analysis of segregant clones obtained from hybrid 158CnpT-1 showed that the primary temperature resistance and high system L transport phenotypes can be segregated from this hybrid independently. The loss of the primary temperature resistance was associated with the loss of the human chromosome 5, as previously reported by other laboratories, whereas the loss of the high leucine transport phenotype, which is associated with a lesser degree of temperature resistance, was correlated with the loss of human chromosome 20.
Mol Cell Biol 1984 Mar
PMID:Characterization of a Chinese hamster-human hybrid cell line with increased system L amino acid transport activity. 671 30

Chinese hamster-human interspecific hybrid cells, which contain human chromosome 5 and express four genes linked on that chromosome, were subjected to selective conditions requiring them to retain one of the four linked genes, leuS (encoding leucyl-tRNA synthetase), but lose another, either emtB (encoding ribosomal protein S14) or chr. Cytogenetic and biochemical analyses of spontaneous segregants isolated by using these unique selective pressures have enabled us to determine the order and regional location of the leuS, hexB, emtB, and chr genes on human chromosome 5. These segregants arise primarily by terminal deletions of various portions of the long arm of chromosome 5. Our results indicate that the order of at least three of these genes is the same on human chromosome 5 and Chinese hamster chromosome 2. Thus, there appears to be extensive homology between Chinese hamster chromosome 2 and human chromosome 5, which represents an extreme example of the conservation of gene organization between very divergent mammalian species. In addition, these hybrids and selective conditions provide a very simple and quantitative means to assess the potency of various agents suspected of inducing gross chromosomal damage.
Mol Cell Biol 1982 Oct
PMID:Selective linkage disruption in human-Chinese hamster cell hybrids: deletion mapping of the leuS, hexB, emtB, and chr genes on human chromosome 5. 717 10

In order to study how Escherichia coli leucyl-tRNA synthetase recognizes tRNA(Leu) and discriminates it from the other two class II tRNAs, tRNA(Ser) and tRNA(Tyr), various mutations were introduced into class II tRNA transcripts. The discriminator base A73, but not the anticodon sequence, was found to serve as a critical recognition element of tRNA(Leu). A base substitution at the invariant nucleotide A14, but not at any of the other nucleotides characteristic of the E. coli tRNA(Leu) isoacceptors among the three class II tRNAs, caused significantly damaged aminoacylation with leucine. A two base-pair deletion in the long variable arm also resulted in no significant decrease of activity. Transplanting the three tertiary elements characteristic of E. coli tRNA(Leu) (i.e. the location of the G18G19 sequence in the D-loop, the A15 U48 base-pair and the stem pairing pattern of the long variable arm) besides the discriminator base change introduced the leucine charging activity in terms of Vmax/Km, up to 0.1 of that for the normal sequence of tRNA(Leu) into both tRNA(Ser) and tRNA(Tyr). These results indicate that A73 and A14 (or its vicinity) are involved in recognition by leucyl-tRNA synthetase, and that several tertiary elements play a significant role in the discrimination of tRNA(Leu) from the other two class II tRNAs.
J Mol Biol 1993 May 20
PMID:Recognition nucleotides of Escherichia coli tRNA(Leu) and its elements facilitating discrimination from tRNASer and tRNA(Tyr). 851 Jan 45

The recognition of tRNALeu, one of the class II tRNAs having a long variable arm, by leucyl-tRNA synthetase in Saccharomyces cerevisiae was studied using the T7 transcription system. Exchanging the anticodon arm of tRNALeu but not the D- or T psi C-arm to that of tRNASer seriously affected the leucine accepting activity. Two nucleotides in the anticodon loop, A35 and G37, were found to be important for leucylation. It was also found that the discriminator base, A73, is required for leucylation, and G73 of tRNASer functions as a negative identity determinant for leucyl-tRNA synthetase. Introducing a set of three base substitutions at positions 35, 37 and 73 was sufficient to convert tRNASer into an efficient leucine acceptor. These results indicate that the identity elements of tRNALeu lie at the second position of the anticodon and the 3' adjacent to the anticodon as well as the discriminator position. Such a sequence specific recognition manner is significantly different from that of Escherichia coli, in which not the anticodon but the tertiary structural elements play a key role in discriminating from other class II tRNAs. The leucine system is the first example which shows that the requirement of the anticodon sequence is variable among species.
J Mol Biol 1996 Nov 15
PMID:The anticodon loop is a major identity determinant of Saccharomyces cerevisiae tRNA(Leu). 894 70

A number of yeasts of the genus Candida translate the standard leucine-CUG codon as serine. This unique genetic code change is the only known alteration to the universal genetic code in cytoplasmic mRNAs, of either eukaryotes or prokaryotes, which involves reassignment of a sense codon. Translation of CUG as serine in these species is mediated by a novel serine-tRNA (ser-tRNACAG), which uniquely has a guanosine at position 33, 5' to the anticodon, a position that is almost invariably occupied by a pyrimidine (uridine in general) in all other tRNAs. We propose that G-33 has two important functions: lowering the decoding efficiency of the ser-tRNACAG and preventing binding of the leucyl-tRNA synthetase. This implicates this nucleotide as a key player in the evolutionary reassignment of the CUG codon. In addition, the novel ser-tRNACAG has 1-methylguanosine (m1G-37) at position 37, 3' to the anticodon, which is characteristic of leucine, but not serine tRNAs. Remarkably, m1G-37 causes leucylation of the ser-tRNACAG both in vitro and in vivo, making the CUG codon an ambiguous codon: the polysemous codon. This indicates that some Candida species tolerate ambiguous decoding and suggests either that (i) the genetic code change has not yet been fully established and is evolving at different rates in different Candida species; or (ii) CUG ambiguity is advantageous and represents the final stage of the reassignment. We propose that such dual specificity indicates that reassignment of the CUG codon evolved through a mechanism that required codon ambiguity and that ambiguous decoding evolved to generate genetic diversity and allow for rapid adaptation to environmental challenges.
Mol Microbiol 1997 Nov
PMID:The non-standard genetic code of Candida spp.: an evolving genetic code or a novel mechanism for adaptation? 940 14

To investigate systematically the RNA sequences necessary for aminoacylation by Escherichia coli leucyl-tRNA synthetase, RNAs with leucylation activity were isolated by in vitro selection from a library of tRNALeu variants possessing randomized sequences in the D-loop, the variable arm, and the T-loop. After two rounds of selection, most of the selected variants showed the following features: (1) the tertiary interaction between nucleotides at positions 15 and 48 was A15-U48; (2) the continuous G18G19 sequence, which is invariant in canonical tRNAs, appeared at the fixed position in the D-loop; and (3) the nucleotide at position 20a in the D-loop was A. These selected nucleotides and their positions, concentrating on the hinge region of tRNA, were identical to those of native tRNALeu. In contrast, although the long variable arm is the most characteristic of the tRNALeu structure, the primary and secondary structures were not correlated with the leucylation activity. These findings indicate that A15-U48, A20a, and G18G19 located at specific positions are involved in the tertiary folding of leucine-accepting tRNA molecules. With increases in the selection cycle, the D-loop sequence and the secondary structure of the variable arm became similar to those of tRNALeu, suggesting that tRNALeu represents an optimized RNA sequence for leucylation.
J Mol Biol 1998 Oct 30
PMID:In vitro selection of RNAs aminoacylated by Escherichia coli leucyl-tRNA synthetase. 978 70

Translation initiation factor IF3, one of three factors specifically required for translation initiation in Escherichia coli, inhibits initiation on any codon other than the three canonical initiation codons, AUG, GUG, or UUG. This discrimination against initiation on non-canonical codons could be due to either direct recognition of the two last bases of the codon and their cognate bases on the anticodon or to some ability to "feel" codon-anticodon complementarity. To investigate the importance of codon-anticodon complementarity in the discriminatory role of IF3, we constructed a derivative of tRNALeuthat has all the known characteristics of an initiator tRNA except the CAU anticodon. This tRNA is efficiently formylated by methionyl-tRNAfMettransformylase and charged by leucyl-tRNA synthetase irrespective of the sequence of its anticodon. These initiator tRNALeuderivatives (called tRNALI) allow initiation at all the non-canonical codons tested, provided that the complementarity between the codon and the anticodon of the initiator tRNALeuis respected. More remarkably, the discrimination by IF3, normally observed with non-canonical codons, is neutralised if a tRNALIcarrying a complementary anticodon is used for initiation. This suggests that IF3 somehow recognises codon-anticodon complementarity, at least at the second and third position of the codon, rather than some specific bases in either the codon or the anticodon.
J Mol Biol 1999 Jul 23
PMID:Discrimination by Escherichia coli initiation factor IF3 against initiation on non-canonical codons relies on complementarity rules. 1039 84

The recognition manner of tRNA(Leu), a class II tRNA characterized by a long variable arm, by leucyl-tRNA synthetase from an extreme halophilic archaea, Haloferax volcanii, was studied using the in vitro transcription system. It was found that the discriminator base (A73) and the long variable arm, especially the specific loop sequence A47CG47D and U47H at the base of this helix, are significant for recognition by LeuRS. An appropriate stem length of the variable arm was also required. Base substitutions in the anticodon arm did not affect the leucylation activity. Transplantation of both the discriminator base and the variable arm of tRNA(Leu) was not sufficient to introduce leucylation activity to tRNA(Ser). Insertion of an additional nucleotide into the D-loop, which is not involved in the direct interaction with LeuRS, converted tRNA(Ser) to an efficient leucine acceptor. This suggests that differences in the tertiary structure play a key role in eliminating tRNA(Ser). The sequence-specific recognition of the long variable arm of tRNA(Leu) has not been observed in any of other organisms reported, such as Escherichia coli, yeast or human. On the other hand, the mode of discrimination from non-cognate tRNAs is similar to that in E. coli in that differences in the tertiary structure play a key role. Similarity extends to the substrate stringency, exemplified by a cross-species aminoacylation study showing that no class II tRNAs from E. coli or yeast can be leucylated by H. volcanii LeuRS. Our results have implications for the understanding of the evolution of the recognition system of class II tRNA.
J Mol Biol 1999 Nov 12
PMID:Unique recognition style of tRNA(Leu) by Haloferax volcanii leucyl-tRNA synthetase. 1054 83

The effect of genistein and daidzein on protein synthesis in osteoblastic MC3T3-E1 cells in vitro was investigated to determine a cellular mechanism by which the isoflavones stimulate bone formation. Cells were cultured for 48 h in alpha-minimal essential medium containing either vehicle, genistein (l0(-7) - 10(-5) M) or daidzein (10(-7) - 10(-5) M). The 5,500 g supernatant of cell homogenate was used for assay of protein synthesis with [3H]leucine incorporation in vitro. The culture with genistein or daidzein caused a significant elevation of protein synthesis in the cell homogenate. The effect of genistein ( 10(-5) M) or daidzein ( 10(-5) M) in elevating protein synthesis was significantly prevented, when cells were cultured for 48 h in a medium containing either actinomycin D (10(-7) M) or cycloheximide (10(-6) M) in the absence or presence of isoflavones. Moreover, when genistein (10(-7) 10(-5) M) or daidzein (10(-6) and 10(-5) M) was added to the reaction mixture containing the cell homogenate obtained from osteoblastic cells cultured without isoflavone, protein synthesis was significantly raised. This increase was markedly blocked by the addition of cycloheximide (10(-7) M). In addition, [3H]leucyl-tRNA synthetase activity in the cytosol of osteoblastic cells was significantly increased by the addition of genistein (10(-6) and 10(-5) M) or daidzein (10(-5) M) into the enzyme reaction mixture. The present study demonstrates that genistein or daidzein can stimulate protein synthesis in osteoblastic MC3T3-E1 cells. The isoflavones may have a stimulatory effect on osteoblastic bone formation due to increasing protein synthesis.
Mol Cell Biochem 2000 Nov
PMID:Stimulatory effect of genistein and daidzein on protein synthesis in osteoblastic MC3T3-E1 cells: activation of aminoacyl-tRNA synthetase. 1119 96


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