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At least 19 recordsLinked to original sources
PubMed1978

Isopentenyladenosine deficient tRNA from an antisuppressor mutant of Saccharomyces cerevisiae.

We have isolated a mutant of Saccharomyces cerevisiae that contains 1.5% of the normal tRNA complement of isopentenyladenosine (i6A). The mutant was characterized by the reduction in efficiency of a tyrosine inserting UAA nonsense suppressor. The chromatographic profiles of tRNATyr and tRNASer on benzoylated DEAE-cellulose are consistent with the loss of i6A by these species. Transfer RNA from the mutant exhibits 6.5% of the cytokinin biological activity expected for yeast tRNA. Transfer RNAs from the mutant that normally contain i6A accept the same levels of amino acids in vitro as the fully modified species. With the exception of i6A, the level of modified bases in unfractionated tRNA from the mutant appears to be normal. The loss of i6A apparently affects tRNA's role in protein synthesis at a step subsequent to aminoacylation.

Adenosine↗
PubMed1978

Antibodies to N6-(delta2-isopentenyl) adenosine and its nucleotide: interaction with purified tRNAs and with bases, nucleosides and nucleotides of the isopentenyladenosine family.

The interaction of antibodies directed toward N6-(delta2-isopentenyl)adenosine, i6Ado, or its nucleotide with related bases, nucleosides, nucleotides and purified tRNAs is described. The selectivity of the antibody preparation was tested in inhibition experiments utilizing a sensitive radioimmunoassay to quantitate the binding of [3H]i6Ado to the antibody. Purified tRNAs containing various modified nucleosides adjacent to the 3'-end of the anticodon were tested to provide information about the selectivity of the antibody preparation toward nucleotides in this position of the tRNA chain. Antibodies directed against the nucleotide hapten were used to purify tRNAs which contain i6Ado and to quantitate the amount of that nucleotide. The same order of selectivity was expressed whether the nucleotides were free or in a tRNA molecule. Interaction of the antibody with compounds from the i6Ado family demonstrated dominance of the hydrophobic isopentenyl group and the importance of positional differences of modifications.

Adenosine↗
PubMed1975

Maturation of a hypermodified nucleoside in transfer RNA.

E. coli C6 rel- met- cys- was cultured in a fully supplemented medium and in media lacking cysteine or methionine. tRNA isolated from the three cultures containted, respectively, a normal complement of modified nucleosides; a deficiency in thiolated nucleosides and a deficiency in methylated nucleosides. Both sulfur-deficient tRNA and methyl-deficient tRNA contained large amounts of N-6- (delta-2-isopentenyl) adenosine and small amounts of the 2-methylthio derivative. Methyl-deficient tRNA contained, in addition a large amount of a cytokinin active, differently modified nucleoside that is believed to be a sulfur derivative of N6-(delta-2-isopentenyl) adenosine. The structure of this compound is unknown. When methly-deficient tRNA and the precusor the tRNA-Tyr su3-+ A25 were enzymatically methylated in vitro, methyl groups were incorporated into derivatives of isopentenyladenosine. These results indicate that the biosynthesis of the 2-methylthio derivative of isopentenyladenosine may occur in a sequential manner, i.e., thiolation of isopentenyladenosine followed by methylation.

Adenosine↗
PubMed1979

Inhibitory effect of cytokinins on PHA-induced human lymphocyte stimulation.

The inhibitory effect of various purine derivatives on PHA-induced human lymphocyte blast formation was studied. Two nucleoside cytokinins, N6-benzyladenosine and N6-isopentenyladenosine, inhibited blast formation at concentrations as low as 10(-6) M. However, the other cytokinins, which lacked the ribosyl residue at N9 position, had to be at the higher molar concentration of 10(-4) before they could induce the same inhibitory effect.

Adenosine↗
PubMed1977

Modification-deficient transfer ribonucleic acids from relaxed control Escherichia coli: structures of the major undermodified phenylalanine and leucine transfer RNAs produced during leucine starvation.

The structures of the major, chromatographically unique phenylalanine and leucine tRNAs produced during leucine starvation of a relaxed control (rel-) mutant of E. coli have been determined. The results demonstrate that the unique species are modification-deficient forms of the major, normally occurring isoacceptor species. The unique tRNAphe differs from the fully modified species at nucleotide positions 16, 37, 39, 47, and 55 from the 5' terminus. The unique species contains uridine (U) in place of dihydrouridine-16 (D16), isopentenyladenosine in place of 2-thiomethyl-N6-(delta2-isopentenyl)adenosine-37, a mixture of U and pseudouridine (psi) in position 39, a mixture of U and 3-(3-carboxypropyl)uridine at position 47, and a mixture of U and psi at position 55. The chromatographically normal isoacceptor from amino acid starved cells is deficient in D16 and psi55, indicating that that species is a mixture of mature and undermodified tRNAs. The unique tRNALeu isoacceptor consists of two subspecies which are undermodified forms of the major, normally occurring isoacceptor, tRNALeuI. Both unique subspecies lack the D and psi residues which occur at positions 16 and 39 from the 5' terminus; one subspecies also lacks D17. Compared with the tRNALeusI from wild-type strains of E. coli B and K12, both tRNALeuI from nonstarved cells and the unique, rel-tRNALeu are deficient in the modified guanosine which normally occurs adjacent to the anticodon and the pseudouridine in the GTpsiC sequence of the psi loop. Both the unique tRNAPhe and the unique tRNALeu lack dihydrouridine residues which occur in the 5' half of the D loop and pseudouridines which occur in the 3' half of the anticodon loop and adjoining stem. Taken together, these findings suggest that the same enzymes are responsible for the formation of these particular modified bases in both tRNAs. The results further suggest that several, perhaps most, of the tRNAs from cells cultured under conditions in which RNA and protein synthesis are uncoupled will be similarly deficient in dihydrouridine and pseudouridine and other minor nucleosides which occur less frequently. Because both modification-deficient rel-tRNAs have dihydrouridine at position 20 and pseudouridine in the psi loop (and at position 41 in the unique tRNALeu), the results support the view that there was multiple D-and psi-forming enzymes in E. coli, some of which may turn over rapidly or are selectively inactivated when protein synthesis is blocked. The results are discussed with a view toward understanding the structural basis for the altered biological activity of the unique tRNAPhe species and the order of events in the posttranscriptional modification of newly synthesized tRNA.

Base Sequence↗
PubMed1978

Alterations in tRNAs containing 2-methylthio-N6-(delta2-isopentenyl)-adenosine during growth of enteropathogenic Escherichia coli in the presence of iron-binding proteins.

Escherichia coli grown in chemically produced iron-deficient media have well characterized alterations in the chromatographic properties of tRNAs containing the modified nucleoside 2-methylthio-N6-(delta2-isopentenyl) adenosine. The present report shows that similar tRNA alterations occur in enteropathogenic E. coli inhibited by human milk and bovine colostrum, the inhibited bacteria containing 10% or less of the normal tRNA species. Adding sufficient iron to saturate the iron-binding capacity of the lactoferrin present in milk and colostrum reversed these changes which are probably due to a failure to methylthiolate the isopentenyladenosine. Although adding iron led to a rapid replacement of abnormal tRNA by the chromatographically normal species, and to a resumption of multiplication, the tRNA alterations are not directly related to the inhibition of growth. Strains of E. coli which grew normally in milk, colostrum and in defined media containing the iron-binding protein transferrin or ovotransferrin also contained about 90% of the abnormal species. Rapid conversion of abnormal tRNA to normal tRNA occurred on adding iron and in the absence of RNA synthesis. The tRNA changes are discussed in relation to their possible connection with both the adaptation of E. coli to growth under the iron-restricted conditions imposed by iron-binding proteins in tissue fluids and with bacterial pathogenicity.

Adenosine↗
PubMed1975

Precursor relationship of phenylalanine transfer ribonucleic acid from Escherichia coli treated with chloramphenicol or starved for iron, methionine, or cysteine.

When treated with chloramphenicol, Escherichia coli 15T minus produces two new species (IV and V) of transfer ribonucleic acid specific for phenylalanine in addition to the major normal species (II) and two minor normal species (I and III), which are seen as distinct components upon fractionation by chromatography on columns of benzoylated diethylaminoethyl-cellulose. Species IV is produced when cells are grown in iron-deficient medium and is, therefore, probably deficient in the 2-methylthio modification of N-6-(delta-2-isopentenyl) adenosine. A new minor species (Va) also appears under those conditions. All of the new components elute earlier than the major normal species. Addition of chloramphenicol to iron-deficient cells leads to the production of species V, and that production is blocked by rifampin, as is the production of species IV. Thus, species IV and V appear to be transcriptional products. Although E. coli 15T minus appears to be rel plus, starvation for methionine or cysteine leads to the accumulation of species IV (without addition of chloramphenicol); rifampin blocks the accumulation. Species V is still produced on addition of chloramphenicol to starved cultures. Starvation for arginine or tryptophan does not alter the chromatographic profile from the normal case. Treatment with permanganate indicates that species II and IV contain isopentenyladenosine but that species V does not. Species V appears to be deficient in both isopentenyl and methylthio modifications of adenosine and perhaps at least one other modification, because removing the isopentenyl moiety from adenosine does not convert species IV into species V, but converts it into species Va. A precursor relationship among species V, VI, and II is suggested by following the chromatographic profile of phenylalanine transfer ribonucleic acid during recovery of E. coli from treatment with chloramphenicol; the various species increase and decrease in a sequential manner.

Adenosine↗
PubMedDate not supplied

Ribose conformations in the common purine(beta)ribosides, in some antibiotic nucleosides, and in some isopropylidene derivatives: a comparison.

With the use of PMR the ribose conformations have been studies in the temperature range -60 to +40 degrees C in ND3 solutions of adenosine (A), guanosine (G), inosine (I), xanthsine (X), purineriboside (PR), 2-aminopurineriboside (2amPR), N6-isopentenyladenosine (N6ipA), 8-bromoadenosine (iA), and isopropylideneguanosine (iG). The aanlysis is based on the two-state S in equilibrium N model of the ribose moiety proposed by Altona and Sundaralingam. The compounds studied can be classified into two groups: 1. A, I, G, X, PR, 2amPR, N6ipA, and T show a small temperature dependence of thnd F have a stronger temperature dependence and [S] approximately 0.8. Within these two groups the similarities observed are greater than observed in the solid state. Some thermodynamic conclusions about the S in equilibrium N and the syn in equilibrium anti equilibria are presented. The results support the previously proposed correlation of the S state of the ribose with the syn conformation of the base and of the N state of the ribose with the anti conformation of the base. Furthermore, it is derived that the gg rotamer is correlated with the S state of the ribose and therefore stabilizes the syn conformation of the base.

Adenosine↗
PubMed1976

Electron impact-induced reactions of N6-(3-methyl-2-butenyl)adenosine and related cytokinins.

Fragmentation reactions of the biologically important N6-(3-methyl-2-butenyl)adenyl moiety have been re-examined with the aid of systematic deuterium labeling in the sidechain and by examination of the 1- and 7-deazanucleoside analogs. It is concluded that the diagnostic reactions which involve expulsion of C3H7 proceed predominantly by ring closure from the sidechain double bond to N-1 (ion a). Base-containing ions m/e 135 and 148 were confirmed to arise mainly by rearrangement of hydrogen from the methyl terminus to N6 and simple cleavage, respectively, but with significant contribution from other pathways involving transfer of sidechain hydrogens to the base.

Adenosine↗